Note: Requesting testing by other experts to confirm the funcationality still works as expected before merging

Note: This will not be compatible with snews_cs until snews-data-formats is integrated into that project as well.

This is a major PR which will introduce breaking changes in exchange for a simplified message creation and validation process, and decoupling between snews_cs and snews_pt.

Here is a summary of the changes:

1. Replace legacy message classes and validation logic with snews-data-formats
2. Some message field names are changed:

• neutrino_time → neutrino_time_utc
• machine_time → machine_time_utc
• sent_time → sent_time_utc
• t_bin_width → t_bin_width_sec
• retract_latest → retract_latest_n

3. Application code present in __init__.py is moved into __main__.py
4. Individual message tests are consolidated into a single file
5. Depcrated patterns are updated (e.g., datetime.utcnow() → datetime.now(UTC))
6. Add pyproject.toml file with pytest configuration
7. General cleanup and tidying (e.g., rearranging imports, whitespace, etc.
8. Updated requirements.txt where necessary (including hop-client -> v.0.10.0)
9. Minimum required Python version bumped from 3.9 to 3.11.

Resolves: #85, #110, #114, #121