fix: harden typing and release publishing

[aiagate]

Summary

• Preserve decorated function signatures and success types with ParamSpec.
• Catch exceptions raised while awaiting async functions decorated with @safe.
• Allow async and_then chains to combine source and subsequent error types as E | F.
• Add the empty-tuple combine_all overload and README executable examples.
• Document AwaitableResult single-consumption semantics and remove stale naming/type ignores.
• Gate PyPI/TestPyPI publishing on Ruff, Pyright, pytest, build/version checks, and isolated wheel installation.
• Reject production pre-release tags via PEP 440 validation; publish only pre-releases to TestPyPI.

Validation

• uv lock --check
• ruff format --check .
• ruff check .
• pyright
• pytest --cov: 93 passed, 0 warnings, 99.48% coverage
• uv build
• Fresh Python 3.13 virtualenv wheel install/import