docs(python): add @example blocks to type stubs and modules

[chaliy]

Summary

• Add docstrings with Example:: blocks to all public methods in _bashkit.pyi
• Update module docstrings in __init__.py, langchain.py, pydantic_ai.py, deepagents.py

Details

Every public method across all classes in the Python type stubs now has a docstring with reStructuredText Example:: block:

• Bash class (constructor, execute, execute_sync, cancel, reset, fs, mount, etc.)
• BashTool class (description, input_schema, output_schema, system_prompt, etc.)
• ScriptedTool class (add_tool, env, execute, etc.)
• FileSystem class (read_file, write_file, mkdir, etc.)
• ExecResult class (to_dict)

Module docstrings updated with usage examples for all integration modules.

Test plan

• ruff check passes
• ruff format --check passes
• Examples use correct reStructuredText format
• Examples match actual API behavior

Closes #1267