Added Python driver tests for coverage

[GumpacG]

Increase gremlin-python test coverage

Adds targeted unit tests for gremlin-python that exercise previously-untested library
code: the explicit-transaction lifecycle (Transaction / execute_in_tx), the GraphBinary
V4 serializer internals (configure_pdt_registry merge and finalize_message byte layout),
the Traversal iteration protocol and traversal.py object model (Traverser,
TraversalStrategies/TraversalStrategy, P/TextP, AtomicInteger, GremlinLang
copy/convert), DriverRemoteConnection/RemoteStrategy wiring and extract_request_options,
the SigV4 auth interceptor, the aiohttp read-timeout normalization (ServerTimeoutError ->
ReadTimeoutError), GraphBinary V4 error branches (unknown type code, long overflow, naive
datetime), and several structure/graph.py object-model / PDT-registry paths. Also adds one
integration test for the server-enforced per-request timeoutMillis. Tests only, no
production code changes.

Coverage (gremlin-python: unit + integration + feature)

Metric	Baseline (master)	With added tests
Line	88.1%	90.0%

Coverage reports

Baseline (master: b907ebb) and with-tests HTML reports were generated with
coverage.py (unit + integration + radish):

With added tests:

Assisted-by: Kiro: Claude Opus 4.8

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.49%. Comparing base (a28cd1f) to head (91df009).
⚠️ Report is 426 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3584      +/-   ##
============================================
+ Coverage     76.35%   76.49%   +0.13%     
- Complexity    13424    14302     +878     
============================================
  Files          1012     1036      +24     
  Lines         60341    64620    +4279     
  Branches       7075     7664     +589     
============================================
+ Hits          46076    49433    +3357     
- Misses        11548    12098     +550     
- Partials       2717     3089     +372     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.