Improve release workflow validation

[marcleblanc2]

Summary

• build both wheel and source distribution during package validation
• allow release reruns for tags reachable from main, not only current main
• validate release runtime dependencies and smoke-test installed wheels from a temp dir

Verification

• uv lock --check
• actionlint
• uv build --wheel --sdist --out-dir /tmp/src-py-lib-build-check --no-create-gitignore
• uv run --frozen python -c 'import src_py_lib; print(src_py_lib.name)'
• git diff --check -- .github/workflows/release.yml .github/workflows/validate.yml