fix: resolve return annotations with from __future__ import annotations

[majiayu000]

Summary

• Fixes issue where @fn decorated functions return strings instead of expected types when using PEP 563 (from __future__ import annotations)
• Uses typing.get_type_hints() to properly resolve string annotations to actual types

Problem

When using from __future__ import annotations, all type annotations become strings by default (PEP 563). The PythonFunction.from_function() method was using sig.return_annotation directly, which would be a string like "Recipe" instead of the actual Recipe class. This caused decorated functions to fail or return wrong types.

Solution

Added annotation resolution using get_type_hints() in PythonFunction.from_function():

• Attempts to resolve string annotations to actual types
• Falls back to the raw annotation if resolution fails (forward references, etc.)

Test plan

• Added unit tests in tests/basic/utilities/test_types_future_annotations.py
• Tests verify return annotations are actual types, not strings
• All existing tests pass (262 passed, 2 skipped)
• Pre-commit checks pass (ruff, ruff-format)

Fixes #950