fix(pool): extended pipeline mixed messages for multi-shard

[meskill]

Fix the issues with multi-shard messages aggregation when multiple parse/describes commands sent in the pipeline.

• proper handle for RowDescription counter to reset state and forward it to the client
• reorganize saving of RowDescription in state to pick the proper RD for validation and decoder
• make sure the decoder gets proper RowDescription and Bind codes when processing the response rows

[codecov]

Codecov Report

❌ Patch coverage is 99.64974% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/backend/pool/connection/aggregate.rs	80.00%	1 Missing ⚠️
...end/client/query_engine/test/pipeline_execution.rs	99.74%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[meskill]

The unit tests and go test should showcase the issue better. The issue appears on multi-shard configuration for requests that try to aggregate things (pgdog/src/backend/pool/connection/multi_shard/mod.rs).

I have doubts about quality of the fix and the code overall in multi_shard and I believe there are other possible issues with it (like ErrorResponse handling, portals handling, anonymous commands), but I hope to fix some of the problems rn and maybe revisit and overhaul the whole flow completely.

[levkk]

Very nice find