[pysrc2cpg] Improve type hint extraction and type recovery from annotations

[allsmog]

Improves Python type recovery precision by leveraging existing type annotations.

• Improve extractTypesFromHint for generics: Optional[str] -> str|None, List[int] -> list, Union[A,B] -> A|B, Dict -> dict, Tuple -> tuple
• Add Python 3.10+ pipe union syntax support (int | str)
• Seed type recovery symbol table from parameter, local, and return type annotations
• Add type stubs for ~45 stdlib builtins (len, str, sorted, etc.) and common stdlib functions (os.path.join, json.loads, etc.)

Test plan

• New type hint propagation tests in TypeRecoveryPassTests
• Updated FunctionDefCpgTests for improved generic resolution
• All existing pysrc2cpg tests pass