Delta remote write metrics: parse commit actions via object_store #177
Description
Summary
Compute exact Delta write metrics (, , etc.) for remote targets (S3/GCS/ADLS) by reading commit logs through object_store.
Context
Current Delta metrics for remote targets intentionally avoid fake values and leave most metrics nullable.
Scope
- Read the written Delta commit JSON () through object_store for remote targets.
- Count actions and sizes.
- Populate accepted output metrics consistently with local Delta.
Acceptance criteria
- Remote Delta reports no longer hardcode placeholder file counts.
- Exact metrics are populated when commit log is readable.
- Fallback remains nullable (not fake values) on partial failures.
Related: #159