Merge #137: Add type-safe channel routing for UserOutput with newtype wrappers

d24db0a refactor: Improve encapsulation with writeln methods (copilot-swe-agent[bot])
470d643 style: Apply rustfmt formatting (copilot-swe-agent[bot])
b49f0dd feat: Add type-safe channel routing with newtype wrappers (copilot-swe-agent[bot])
5016d98 Initial plan (copilot-swe-agent[bot])

Pull request description:

  Channel routing (stdout vs stderr) in `UserOutput` was done via runtime pattern matching. This adds compile-time guarantees using newtype wrappers to prevent accidental channel confusion.

  ## Changes

  **Type-Safe Wrappers** (private)
  - `StdoutWriter` and `StderrWriter` newtypes wrapping `Box<dyn Write + Send + Sync>`
  - Methods: `new()`, `write_line()`, `writeln()`
  - Zero-cost abstraction via newtype pattern

  **UserOutput Structure**
  - Fields changed from `Box<dyn Write>` to typed wrappers (`stdout: StdoutWriter`, `stderr: StderrWriter`)
  - Private helpers `write_to_stdout()` and `write_to_stderr()` for type-safe dispatch
  - `write()` method now uses compile-time channel routing instead of runtime matching

  **Example**

  Before (runtime dispatch):
  ```rust
  let writer = match message.channel() {
      Channel::Stdout => &mut self.stdout_writer,
      Channel::Stderr => &mut self.stderr_writer,
  };
  write!(writer, "{formatted}").ok();
  ```

  After (type-safe dispatch):
  ```rust
  match message.channel() {
      Channel::Stdout => self.write_to_stdout(&formatted),
      Channel::Stderr => self.write_to_stderr(&formatted),
  }
  ```

  **Compatibility**
  - All existing tests pass without modification
  - Public API unchanged
  - Added 8 tests demonstrating compile-time safety

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  <details>

  <summary>Original prompt</summary>

  ----

  *This section details on the original issue you should resolve*

  <issue_title>Type-Safe Channel Routing for User Output</issue_title>
  <issue_description>## Overview

  Add compile-time type safety for channel routing (stdout vs stderr) in the `UserOutput` module by introducing newtype wrappers for writers. Currently, channel routing is done with runtime pattern matching which, while functional, doesn't provide compile-time guarantees that messages go to the correct channel.

  This refactoring introduces `StdoutWriter` and `StderrWriter` newtype wrappers that make channel routing explicit in the type system, preventing accidental channel confusion at compile time.

  ## Specification

  See detailed specification: [docs/issues/135-type-safe-channel-routing-for-user-output.md](https://github.com/torrust/torrust-tracker-deployer/blob/main/docs/issues/135-type-safe-channel-routing-for-user-output.md)

  ## 🏗️ Architecture Requirements

  **DDD Layer**: Presentation
  **Module Path**: `src/presentation/user_output.rs`
  **Pattern**: Type-safe wrappers using newtype pattern

  ### Module Structure Requirements

  - [ ] Follow module organization conventions (see [docs/contributing/module-organization.md](https://github.com/torrust/torrust-tracker-deployer/blob/main/docs/contributing/module-organization.md))
  - [ ] Keep writer wrappers private as implementation details
  - [ ] Maintain public API compatibility with existing code

  ### Architectural Constraints

  - [ ] Zero-cost abstraction using newtype pattern
  - [ ] No runtime overhead compared to current implementation
  - [ ] Preserve existing error handling behavior
  - [ ] Error handling follows project conventions (see [docs/contributing/error-handling.md](https://github.com/torrust/torrust-tracker-deployer/blob/main/docs/contributing/error-handling.md))

  ### Anti-Patterns to Avoid

  - ❌ Exposing writer wrappers in public API unnecessarily
  - ❌ Adding runtime checks when compile-time safety is available
  - ❌ Breaking existing test infrastructure

  ## Implementation Plan

  ### Phase 1: Create Newtype Wrappers (30 minutes)

  - [ ] Task 1.1: Create `StdoutWriter` newtype struct with documentation
  - [ ] Task 1.2: Create `StderrWriter` newtype struct with documentation
  - [ ] Task 1.3: Implement `new()` constructor for both wrappers
  - [ ] Task 1.4: Implement `write_line()` method for both wrappers
  - [ ] Task 1.5: Add unit tests for wrapper creation and writing

  ### Phase 2: Update UserOutput Structure (45 minutes)

  - [ ] Task 2.1: Update `UserOutput` struct fields to use typed wrappers
  - [ ] Task 2.2: Add private helper methods `write_to_stdout()` and `write_to_stderr()`
  - [ ] Task 2.3: Update all constructors to wrap writers in typed newtype
  - [ ] Task 2.4: Update `write()` method to use typed writer helpers
  - [ ] Task 2.5: Verify all existing public methods compile and work correctly

  ### Phase 3: Update Tests (30 minutes)

  - [ ] Task 3.1: Update test infrastructure to work with newtype wrappers
  - [ ] Task 3.2: Add tests for type-safe channel routing
  - [ ] Task 3.3: Verify all existing tests pass without modification
  - [ ] Task 3.4: Add test cases demonstrating compile-time safety benefits

  ### Phase 4: Documentation and Quality (30 minutes)

  - [ ] Task 4.1: Update module documentation to mention type-safe routing
  - [ ] Task 4.2: Add code examples showing type safety benefits
  - [ ] Task 4.3: Run pre-commit checks and fix any issues
  - [ ] Task 4.4: Verify documentation builds correctly

  ## Acceptance Criteria

  > **Note for Contributors**: These criteria define what the PR reviewer will check. Use this as your pre-review checklist before submitting the PR to minimize back-and-forth iterations.

  **Quality Checks**:

  - [ ] Pre-commit checks pass: `./scripts/pre-commit.sh`
  - [ ] All tests pass: `cargo test`
  - [ ] Documentation builds: `cargo doc --no-deps`

  **Task-Specific Criteria**:

  - [ ] `StdoutWriter` and `StderrWriter` newtype wrappers are implemented
  - [ ] Both wrappers have `new()` and `write_line()` methods
  - [ ] `UserOutput` struct uses typed wrappers instead of raw `Box<dyn Write>`
  - [ ] All constructors wrap raw writers in typed newtypes
  - [ ] Private helper methods `write_to_stdout()` and `write_to_stderr()` exist
  - [ ] The `write()` method uses typed helpers instead of direct writer access
  - [ ] All existing tests pass without modification
  - [ ] New tests demonstrate compile-time safety benefits
  - [ ] Module documentation is updated to reflect type-safe routing
  - [ ] Code examples show the benefits of the newtype pattern
  - [ ] No performance regression (zero-cost abstraction)
  - [ ] IDE autocomplete shows channel-specific methods

  ## Related

  - Parent: #102 (Epic: User Output Architecture Improvements)
  - Specification: docs/issues/135-type-safe-channel-routing-for-user-output.md
  - Refactoring Plan: [docs/refactors/plans/user-output-architecture-improvements.md](https://github.com/torrust/torrust-tracker-deployer/blob/main/docs/refactors/plans/use...

  </details>

  - Fixes #135

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ACKs for top commit:
  josecelano:
    ACK d24db0a

Tree-SHA512: 9e916c8e7dfa799e9314bf7f0d8925cfd24d584c85ee395acf166f0a5d736867f2ead9f9dc3bea1c0359305f8ebaefe859c9a9c73a3e9835cd4f1bf278388c4b

Author: josecelano