fix(python3): replace six shims and fix deprecation warnings [VC-55627]

[ndevarapalli-panw]

Summary

• Replace six library with native Python 3 equivalents (str, bytes, urllib.parse) — unnecessary since Python ≥ 3.9.2 is already required
• Fix datetime.utcnow() deprecated in Python 3.12 with datetime.now(timezone.utc)
• Fix cert.not_valid_after deprecated in cryptography 42+ with cert.not_valid_after_utc
• Fix e.message / err.message in error handlers (causes AttributeError on Python 3 when triggered)

Test plan

• 41/41 unit tests pass with -W error (warnings-as-errors) - no deprecation warnings remain
• Replacements verified semantically identical at runtime before applying

Closes VC-55627