feat(sql): add S3 Select command with probe and streaming support

[GatewayJ]

Related

• Adds Phase-2 SQL capability discussed in local work branch.

Background

rc did not have a dedicated command for S3 Select queries on objects. Users had no direct CLI path to run SelectObjectContent across S3-compatible backends.

What Changed

• Added new command: rc sql
• Added core Select domain types and trait hooks:
  • SelectOptions, SelectInputFormat, SelectOutputFormat, SelectCompression
  • ObjectStore::probe_select_support
  • ObjectStore::select_object_content
• Added S3 implementation for:
  • request mapping to AWS SDK SelectObjectContent
  • event-stream record forwarding to stdout writer
  • backend support probing and error classification
• Wired command routing/help contract updates.

Validation

All required checks passed locally:

• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace

Notes

• Rebasing conflicts were resolved against latest origin/main before publishing.

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