feat: support logging to stderr in Jupyter Notebook environments (#156)

[dgenio]

Summary

Fixes #156 - Adds support for displaying stderr output in Jupyter Notebook environments.

Changes

• Added Jupyter/IPython detection using IPython.get_ipython()
• Implemented async stderr reader that reads stderr asynchronously (similar to stdout)
• Added IPython display integration for colored stderr output in Jupyter notebooks
• Updated process creation to pipe stderr instead of redirecting (enables async reading)
• Updated Windows process creation and fallback to support piped stderr
• Updated FallbackProcess to wrap stderr in async-compatible streams

Design Decisions

• Backward compatibility: errlog parameter is kept but behavior adapts based on environment
• Error handling: Non-critical errors are logged but don't stop execution
• Performance: Matches stdout_reader behavior (line-by-line buffering)
• Platform support: Works on both Unix and Windows (including fallback path)

Testing

• Added comprehensive tests for stderr capture, Jupyter detection, and display integration
• All existing tests pass
• Linting and type checking pass

Behavior

• In Jupyter: stderr is displayed using IPython's display system with red HTML formatting
• Outside Jupyter: stderr is printed to the provided errlog stream (defaults to sys.stderr)
• Fallback: If IPython display fails, falls back to regular print

This enables proper debugging of MCP servers in Jupyter notebook environments, addressing the issue where server crashes or command errors were invisible.