feat: add configurable batch size for bulk inserting failed rsources records

[mihir20]

Description

Txn Inserting into rsources_failed_keys_v2_records is taking too much time. The core bottleneck is AddFailedRecords() for rsources_stats. It uses tx.Prepare + a loop of individual stmt.ExecContext calls. Each ExecContext is a separate network round-trip to Postgres. If a batch
has 1,000 aborted jobs with record_ids, that's 1,000 sequential INSERT round-trips all within one transaction.

• Introduced batch processing for inserting failed records in rsources_failed_keys_v2_records
• Added FailedRecordsInsertBatchSize configuration to control batch size
• Implemented batch insert SQL statement construction
• Updated unit tests to cover multi-batch scenarios
• Ensured default batch size is set when configuration is invalid

We could have used the COPY command, but the insert needs ON CONFLICT (id, record_id) DO UPDATE SET ts = NOW(), and COPY doesn't support ON CONFLICT

Linear Ticket

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.66%. Comparing base (f0bdc52) to head (e049597).

Files with missing lines	Patch %	Lines
services/rsources/handler.go	96.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6873      +/-   ##
==========================================
- Coverage   80.08%   79.66%   -0.42%     
==========================================
  Files         565      565              
  Lines       63308    63323      +15     
==========================================
- Hits        50698    50447     -251     
- Misses       9619     9897     +278     
+ Partials     2991     2979      -12     

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[atzoum]

need an upper limit based on the max number of parameters allowed

[ktgowtham]

LGTM