feat(requests): Raise clear errors if requests_wrapper is missing; update docs

[diego-coder]

Addresses: #30498

Summary

This PR improves the usability and error handling of the RequestsTool family by providing explicit, user-friendly errors when required arguments are missing, and by enhancing documentation for both contributors and users.

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Motivation

Previously, initializing any RequestsTool (such as RequestsGetTool) without the required requests_wrapper argument resulted in a generic and potentially confusing Pydantic ValidationError.

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What's Changed

• Code Fix:
  A Pydantic @model_validator has been added to the BaseRequestsTool. It now proactively checks for the required requests_wrapper argument and raises a clear, user-friendly ValueError if it's missing. This fix is inherited by all request tools (GET, POST, etc.).

• Documentation Fix:
  The docstring for RequestsGetTool has been improved to include a .. warning::, a clear usage example, and a Google-style Args: section detailing the required parameters.

• Testing:
  Added a unit test (test_requests_tool_missing_wrapper_raises_error) to ensure that the new error handling triggers as intended if requests_wrapper is not provided.

• Formatting and Linting:
  All affected files have been formatted and linted to match project standards (ruff format and ruff check --fix).

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Example Usage

from langchain_community.tools import RequestsGetTool
from langchain_community.utilities import TextRequestsWrapper

# Correct usage: must provide a requests_wrapper
wrapper = TextRequestsWrapper()
tool = RequestsGetTool(
    requests_wrapper=wrapper,
    allow_dangerous_requests=True
)

If the required requests_wrapper is omitted, the following error is now raised:

ValueError: `requests_wrapper` is a required argument for this tool. Please pass in an instance of a RequestsWrapper, e.g. `TextRequestsWrapper()`.

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Checklist

• Added or updated docstrings for all affected classes/functions
• Added unit test for new error handling
• Code is formatted and linted to project standards (ruff format / ruff check --fix)
• All tests pass locally (pytest)

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Closes

Closes #214