chore: add D212 lint rule to enforce Google-style docstrings

[felixweinberger]

Summary

Adds the D212 ruff rule to enforce that multi-line docstring summaries start on the first line (Google-style).

Motivation and Context

Enforces consistent docstring formatting across the codebase. The Google convention requires the summary to be on the same line as the opening """:

# Good (D212 compliant)
def foo():
    """Do something useful.
    
    More details here.
    """

# Bad (D212 violation)  
def foo():
    """
    Do something useful.
    
    More details here.
    """

Fixes #1890

How Has This Been Tested?

• uv run ruff check . passes
• uv run pyright passes

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed