Resolve datetime deprecation warnings

[emmanuel-ferdman]

PR Summary

This PR fixes the DeprecationWarning that appears in Python 3.12+ when using datetime.utcnow(). It replaces it with a more future-proof approach: datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None). This keeps the datetime object naive (without timezone info), which is important for parts of the code that expect it that way, but avoids the warning by using a timezone-aware method first:

# Before (deprecated)  
from datetime import datetime  
naive_time = datetime.utcnow()  # Raises warning  

# Common Fix (timezone-aware)  
from datetime import datetime, timezone  
aware_time = datetime.datetime.now(datetime.timezone.utc)  # Breaks naive-dependent code  

# This PR's Fix (naive but compliant)  
from datetime import datetime, timezone  
compliant_time = datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None)  # No warning, backward-compatible  

You can see those warnings in the latest CI run:

  D:\a\boofuzz\boofuzz\boofuzz\fuzz_logger_csv.py:24: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
    s = datetime.datetime.utcnow().isoformat()

unit_tests/test_session_failure_handling.py::TestNoResponseFailure::test_no_response_causes_restart
  D:\a\boofuzz\boofuzz\boofuzz\sessions\session.py:174: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
    self._run_id = datetime.datetime.utcnow().replace(microsecond=0).isoformat().replace(":", "-")

[SR4ven]

Thank you for the contribution @emmanuel-ferdman!