Problem

The pack writer (PackWriter) currently stores full objects only — no OFS_DELTA or REF_DELTA entries are generated. This means packfiles produced by this library are 3-10x larger than what git repack would produce.

Impact

• Wire transfers (push/fetch) send far more data than necessary
• Storage consumption is significantly higher than standard git
• Interop with bandwidth-constrained clients suffers

Acceptance Criteria

• Pack writer generates OFS_DELTA entries for similar objects
• Delta compression ratio is within 2x of git repack for typical repos
• git verify-pack still passes on generated packs
• Existing tests continue to pass
• Benchmarks added comparing pack sizes with/without delta compression