Update GitHub Actions to Node 24 releases

[fruwe]

Closes #63

Summary

• pin every official GitHub Action in the test and release workflows to the approved immutable Node 24-based commit
• preserve Python 3.13, the specification and conformance pins, package version 0.0.6, and PyPI Trusted Publishing behavior

Validation

• parsed both workflow YAML files with yq
• confirmed all official actions use the approved immutable commits and no stale version references remain
• .venv/bin/ruff check .
• .venv/bin/mypy src/determa
• .venv/bin/pytest -q (175 passed)
• .venv/bin/pytest conformance -q (93 passed across the merged 88-case suite)
• git diff --check

Exclusions

• no package version bump, tag, release, or publishing change