fix(connectors): fix postgres source CDC producing no messages

[mattp5657]

Which issue does this PR address?

Relates to #3582

Rationale

Builtin CDC mode currently produces zero messages against a real
database - wrong plugin/read-path pairing, and a parser matching a
format no real Postgres output plugin emits. This PR is scoped to
getting CDC actually working and provably correct, nothing more.

I have reduce the scope of this specific PR for reviewability, in the future
would look to create issues and work on these issues:

• pgoutput as the long-term plugin - real binary decoder + streaming
  connection is a much bigger lift; test_decoding unblocks correctness
  today. Target once cdc_backend = "pg_replicate" gets picked up.
• At-least-once / crash safety (slot advances before send is confirmed,
  no LSN tracked) - needs its own review since it touches the
  state-persistence contract. Follow-up: #TODO.
• Cosmetic items (UUID vs PK as message id, processing time vs WAL
  commit time, old_data unpopulated) - mechanical, separate PR.

What changed?

Before: wrong slot plugin, a parser matching a format no real Postgres
output emits, and invalid setup SQL - CDC produced zero messages, and
several related bugs failed silently too. After: parser rewritten
against real captured output, setup/poll SQL fixed and bounded, and
those failure modes now work correctly or fail loudly. Covered by
corpus-driven unit tests plus integration tests against a live
wal_level=logical container.

• Parser rewritten against real test_decoding output
• Slot/setup SQL fixed, including the upgrade path and table filtering
• Batch handling hardened (bad rows, unbounded backlog)
• Dead config fields removed

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

Claude was used to help generate and review this PR.

[codecov]

Codecov Report

❌ Patch coverage is 94.57364% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.98%. Comparing base (700221b) to head (2f77f92).

Files with missing lines	Patch %	Lines
core/connectors/sources/postgres_source/src/lib.rs	94.57%	27 Missing and 8 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3640       +/-   ##
=============================================
- Coverage     74.35%   40.98%   -33.37%     
  Complexity      950      950               
=============================================
  Files          1303     1301        -2     
  Lines        148712   129522    -19190     
  Branches     124221   105033    -19188     
=============================================
- Hits         110569    53089    -57480     
- Misses        34668    73663    +38995     
+ Partials       3475     2770      -705     

Components	Coverage Δ
Rust Core	33.00% <94.57%> (-41.59%)	⬇️
Java SDK	62.64% <ø> (ø)
C# SDK	72.20% <ø> (-0.07%)	⬇️
Python SDK	92.27% <ø> (ø)
PHP SDK	84.52% <ø> (ø)
Node SDK	92.82% <ø> (+0.21%)	⬆️
Go SDK	43.08% <ø> (ø)

Files with missing lines	Coverage Δ
core/connectors/sources/postgres_source/src/lib.rs	73.20% <94.57%> (+16.52%)	⬆️

... and 424 files with indirect coverage changes

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[hubcio]

i think this is somewhat related to #3313

[hubcio]

@mmodzelewski could you please check this one?

[mmodzelewski]

Thanks, @mattp5657. The change looks solid, I've posted a few comments where the code could be improved.

[mattp5657]

These should be fixed, let me know if you have any other feedback :)

[mattp5657]

/ready

[mmodzelewski]

Thanks, @mattp5657, approved