Add StrictSerializableRW Query mode and commit timestamps

[vgvoleg]

Add QueryStrictSerializableReadWrite for Query transactions and expose the optional VirtualTimestamp from explicit commits and the trailing ExecuteQuery response. A streamed timestamp becomes available after the result stream is fully consumed.

Timestamp comparisons use unsigned plan_step, then tx_id, and require matching configured endpoint and database path. The SDK cannot establish database identity beyond those settings, so it rejects comparisons when they differ or are unavailable.

The pinned ydb-api-protos revision and all generated protobuf variants already contain the required fields; no stub regeneration is needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.81%. Comparing base (5fb97b3) to head (b2e72b7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #910      +/-   ##
==========================================
+ Coverage   82.67%   82.81%   +0.13%     
==========================================
  Files          99       99              
  Lines       12957    13044      +87     
  Branches     1269     1281      +12     
==========================================
+ Hits        10712    10802      +90     
+ Misses       1794     1793       -1     
+ Partials      451      449       -2     

Flag	Coverage Δ
integration	80.45% <79.56%> (+0.01%)	⬆️
unit	49.93% <100.00%> (+0.84%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ydb/_grpc/grpcwrapper/ydb_query.py	99.06% <100.00%> (+<0.01%)	⬆️
ydb/_grpc/grpcwrapper/ydb_query_public_types.py	89.18% <100.00%> (+4.57%)	⬆️
ydb/aio/query/base.py	100.00% <100.00%> (ø)
ydb/aio/query/transaction.py	100.00% <100.00%> (ø)
ydb/query/__init__.py	81.25% <ø> (ø)
ydb/query/base.py	96.13% <100.00%> (+0.87%)	⬆️
ydb/query/transaction.py	91.79% <100.00%> (+1.50%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.