python-decorator: bump to 5.2.1

python-decorator: bump to 5.2.1

Changes since 4.4.2:
- v5.x rewrites the implementation using the standard library
  inspect module, dropping the code generation approach
- Signature preservation is now based on functools.wraps internals
- New contextmanager and asynccontextmanager decorator support
- Python 3.8+ required; Python 2 no longer supported

Also add test.sh to verify signature preservation and basic usage.

Link: https://github.com/micheles/decorator/blob/master/CHANGES.md
Signed-off-by: Alexandru Ardelean <redacted>