refactor(connectors): extract row-processing logic into reusable process_row method

[atharvalade]

Which issue does this PR close?

Closes #3173

Rationale

Row-processing logic lived inline in poll_tables, making it impossible to reuse across future parallel/chunked polling paths without duplication.

What changed?

The column-iteration, value-extraction, JSON-payload construction, and ProducedMessage assembly were tightly coupled inside poll_tables's inner loop (~80 lines). Any new polling variant (parallel, chunked) would need to copy-paste this block.

Extracted a process_row method that accepts a RowProcessingConfig (table, tracking/pk columns, format flags) and returns a ProcessedRow (message + offset + pk). The poll_tables loop now delegates to this single-responsibility method in ~12 lines.

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

1. Opus 4.6
2. used for exploration and implementation guidance
3. Verified via cargo check, clippy -D warnings, fmt --check, all 19 unit tests passing, CI lint scripts passing
4. Yes, all code can be explained

[codecov]

Codecov Report

❌ Patch coverage is 0% with 87 lines in your changes missing coverage. Please review.
✅ Project coverage is 18.36%. Comparing base (638e5fb) to head (f6a651f).

Files with missing lines	Patch %	Lines
core/connectors/sources/postgres_source/src/lib.rs	0.00%	87 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (50.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3198       +/-   ##
=============================================
- Coverage     74.18%   18.36%   -55.83%     
  Complexity      943      943               
=============================================
  Files          1200     1191        -9     
  Lines        109618    94753    -14865     
  Branches      86508    71780    -14728     
=============================================
- Hits          81323    17401    -63922     
- Misses        25548    76953    +51405     
+ Partials       2747      399     -2348     

Components	Coverage Δ
Rust Core	0.89% <0.00%> (-74.53%)	⬇️
Java SDK	60.14% <ø> (+1.70%)	⬆️
C# SDK	69.43% <ø> (ø)
Python SDK	81.43% <ø> (ø)
Node SDK	91.53% <ø> (ø)
Go SDK	39.68% <ø> (-0.24%)	⬇️

Files with missing lines	Coverage Δ
core/connectors/sources/postgres_source/src/lib.rs	40.78% <0.00%> (-26.40%)	⬇️

... and 693 files with indirect coverage changes

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[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs.

If you need a review, please ensure CI is green and the PR is rebased on the latest master. Don't hesitate to ping the maintainers - either @core on Discord or by mentioning them directly here on the PR.

Thank you for your contribution!

[hubcio]

/ready