Integrate wasmcov for WASM code coverage

[RAprogramm]

Problem

Currently, WASM-specific code is not included in coverage reports due to Rust tooling limitations:

• cargo-llvm-cov only supports native platforms (x86_64)
• wasm-bindgen-test coverage is experimental
• cargo-tarpaulin does not support wasm32

This results in incomplete coverage metrics and a warning in README.

Solution

Integrate wasmcov - a specialized tool for WASM code coverage analysis developed by Hacken.

Implementation Plan

1. Add wasmcov dependency

   • Add wasmcov = "0.2" to dev-dependencies
   • Add capture_coverage function to library

2. Create dedicated CI job

   • Use nightly Rust toolchain (required by wasmcov)
   • Run cargo wasmcov test for WASM tests
   • Generate LLVM coverage reports

3. Merge coverage reports

   • Keep existing cargo-llvm-cov for native code
   • Add wasmcov reports for WASM code
   • Combine in Codecov

4. Update documentation

   • Remove coverage limitations warning from README
   • Update coverage metrics
   • Document wasmcov usage

Expected Outcomes

• Coverage metrics will include WASM-only modules
• True coverage should reach 95%+ target
• Close issue WASM code testing and coverage strategy #128

Technical Details

• Tool: https://github.com/hknio/wasmcov
• Requires: nightly Rust, LLVM tools
• Used by: Radix, NEAR Protocol

Closes #128