fix: Improve HULC timestamp counter with overflow detection and clock drift protection

[bvanelli]

Summary

• Add ActualOverflowError for when the HULC counter exceeds 0xFFFF within the same millisecond
• Protect against clock drift by ensuring logical time never goes backward
• Truncate timestamps to millisecond precision to match Node.js behavior
• Refactor MessageEnvelope to expose a .message() helper, reducing duplication in SyncResponse.get_messages()

Closes #194

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.64%. Comparing base (88d5780) to head (9102b61).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #196   +/-   ##
=======================================
  Coverage   97.64%   97.64%           
=======================================
  Files          21       21           
  Lines        3222     3231    +9     
=======================================
+ Hits         3146     3155    +9     
  Misses         76       76           

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