multi-get: expose rocksdb multi-get api do batch get

[zhangjinpeng87]

Expose rocksdb's multi-get interface to do batch get.

Summary by CodeRabbit

• New Features
  • Added multi-key batch retrieval functionality enabling efficient fetching of multiple values in a single operation.
  • Support for bulk retrieval across column families with fine-grained error handling for individual keys.
  • New API methods provide streamlined access to multiple key-value pairs with per-key result status.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request adds batch retrieval (multi-get) functionality to RocksDB Rust bindings. New FFI functions crocksdb_multi_get and crocksdb_multi_get_cf are introduced for handling multiple keys in a single call. Corresponding Rust wrapper methods are implemented on DB and Snapshot types to expose ergonomic APIs for bulk key retrieval operations with proper error handling and memory management.

Changes

Cohort / File(s)	Summary
FFI Bindings librocksdb_sys/src/lib.rs	Two new extern "C" functions added: crocksdb_multi_get (batch retrieval without column families) and crocksdb_multi_get_cf (batch retrieval with column families). Both accept arrays of keys and return arrays of values with per-key error handling.
Rust API Wrappers src/rocksdb.rs	Multi-get methods added to Snapshot<D> (multi_get, multi_get_cf). Four methods added/updated in DB impl (multi_get_opt, multi_get, multi_get_cf_opt, multi_get_cf). Internal helper build_multi_get_result marshals FFI outputs into Rust Result types and manages memory cleanup.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Poem

🐰 whiskers twitch with joy
Batch gets hopping without delay,
Multi-keys retrieved in a single way,
Snapshots and databases aligned,
Efficiency gains of every kind! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 31.25% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: exposing RocksDB's multi-get API for batch retrieval operations, which aligns with the additions of multi_get and multi_get_cf functions.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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