Overhaul datastore with query fixes, logging, and tests

[dbarbashov]

While I was trying to find a reason why s3 store started losing blocks (ipld block not found error). I've played around with the repo and it seems that after few guided vibe-coding iterations it finally became stable. There were several issues with pagination/key handling logic which were addressed.

Potentially this fixes #261. At least it fixed it for me on my node

Key changes:

• Correctness Fixes:

  • Query Implementation: The Query method has been completely rewritten to be a stateful iterator.
    • It now correctly handles pagination for prefixes that span multiple S3 ListObjectsV2 pages. The previous implementation was limited to a single page of results (max 1000 objects).
    • Offset and Limit are now properly supported across paginated results.
  • Batch Operations: Batch Delete operations now correctly prefix keys with the configured RootDirectory before sending them to S3.
  • Key Path Handling: Key paths are now more robustly handled by consistently trimming leading slashes, aligning with go-datastore conventions.

• Refactoring & Testability:

  • S3 Interface: The S3 client is now abstracted behind the s3iface.S3API interface.
  • New Unit Tests:
    • Batch operations (Put and Delete)
    • Query pagination, Offset, and Limit
    • Error handling and delete idempotency

• Observability & Dependencies:

  • Comprehensive Logging: Added structured logging via go-log/v2 to all key datastore operations (Put, Get, Query, Batch, etc.).
  • Dependency Updates: Updated all Go module dependencies to their latest versions, including kubo and go-datastore, and bumped the Go version to 1.25.
  • Housekeeping: Updated .gitignore with common editor and OS patterns.