[PR #1189/7aaf53fc backport][3.27] Fix repair_metadata OOM on large repositories

[patchback]

This is a backport of PR #1189 as merged into main (7aaf53f).

Summary

• Reduce BULK_SIZE from 1000 to 250, flushing batches 4x more often to cap peak memory
• Eliminate double S3 read per wheel by reusing the temp file from metadata extraction for metadata artifact creation
• Explicitly close artifact file handles after each iteration to release S3 buffer memory

Fixes #1188

Test plan

• Existing test_repair.py tests pass (metadata repair command, endpoint, artifact repair)
• New test_metadata_repair_batch_boundary passes with reduced BULK_SIZE
• Deploy to stage and run repair-python-metadata.py --env stage --domain <large-domain> to verify no OOM

JIRA: PULP-1573

🤖 Generated with Claude Code