RSCAN command implementation

[iwanbk]

No description provided.

[Copilot]

Pull Request Overview

This pull request implements the new RSCAN command by updating the metadata tree scanning API to support bidirectional scanning. Key changes include:

• Updating the iter_kv API to include an optional ScanDirection parameter.
• Renaming the scanning parameter in Namespace from start_after to start_key.
• Adjusting test cases and multiple store implementations to align with the new API signature.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
s3cas/src/cas/fs.rs	Updated iter_kv call to include an extra None parameter.
respd/src/storage.rs	Updated iter_kv invocation with the new parameter.
respd/src/namespace.rs	Renamed parameter and added a ScanDirection option in scan.
respd/src/cmd.rs	Updated scan method invocation to pass the new parameter.
metastore/src/traits.rs	Modified iter_kv signature and added ScanDirection documentation.
metastore/src/stores/test_utils.rs	Adjusted iter_kv calls in test utilities to the new API signature.
metastore/src/stores/fjall_notx.rs	Updated iter_kv implementation to support directional scanning.
metastore/src/stores/fjall.rs	Updated iter_kv implementation with new parameter handling.
metastore/src/meta_store.rs	Updated iter_kv call in bucket listing to include the new parameter.

[Copilot]

Pull Request Overview

This PR implements the RSCAN command to scan keys in backward order. Key changes include adding integration tests for RSCAN, extending the namespace API with a scan_backward method, updating command parsing and handling to support RSCAN, and documenting the new command.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
respd/tests/integration_test.rs	Added integration tests covering various RSCAN scenarios
respd/src/namespace.rs	Updated scan API; added scan_backward for reverse scanning
respd/src/cmd.rs	Introduced RSCAN command and its handler
respd/README.md	Documented the new RSCAN command
metastore/src/traits.rs	Added iter_kv_backward to trait definition
metastore/src/stores/fjall_notx.rs	Implemented iter_kv_backward for backward scanning in FjallTreeNotx
metastore/src/stores/fjall.rs	Implemented iter_kv_backward for backward scanning in FjallTree

Comments suppressed due to low confidence (2)

respd/src/cmd.rs:938

• [nitpick] For consistency with the scan_backward API, consider renaming the 'start_after' variable to 'start_key'.

let start_after = cursor.map(|c| c.into_bytes());

metastore/src/stores/fjall.rs:288

• [nitpick] Consider using a more explicit unbounded range construct (if supported) or adding a clarifying comment to explain the use of '..Vec::new()' for backward scanning.

None => ..Vec::new(), // Start from the end