Xrootdpyfs

- stable release
- fs: align error code changes (3005, 3018) to comply with
https://github.com/xrootd/xrootd/commit/3715a81a5807a2fd2aee5dbbcd2aac1a74d5acc6

- upgrade xrootd to version 5.
- fix testing xrootd responses

- Upgrade pyfs to version 2.
- Improve module's files organization and code formatting.

- Supports `xrootd4.12.7`
- Adds GH publish flow
- Fixes tests with python 3
- Adds `__len__` method in `XRootDPyFile`

- Fixes a Python 3 compatibility issue in xrd_checksum().
- Pins XRootD version <5 due to compatibility issues with v5+.

- Adds Python 3 support.