feat(mito2): add partition range cache infrastructure

[evenyag]

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What's changed and what's your intention?

This PR adds the infrastructure for partition range scan result caching in mito2.

The main changes are:

• add a dedicated range result cache to CacheManager and expose it through CacheStrategy
• introduce read/range_cache.rs to define cache keys, request fingerprints, cached values, and
  memory estimation
• add scan fingerprint construction in scan_region.rs for cache-eligible reads
• include schema-sensitive fields in the fingerprint, including read column types and
  partition_expr_version
• add unit tests for cache behavior and fingerprint eligibility/normalization
• derive Hash for MergeMode so it can participate in cache keys

This branch is intentionally infrastructure-focused. It prepares the cache key model and cache
container, but it does not yet wire the scan execution path to actually read from or write to the
new range result cache.

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the foundational infrastructure for caching partition range scan results within the mito2 storage engine. It establishes the necessary data structures for cache keys and values, integrates a new cache type into the existing CacheManager and CacheStrategy, and provides a mechanism to generate unique fingerprints for scan requests. This setup is a prerequisite for future work that will wire the actual scan execution path to utilize this new caching layer, aiming to improve read performance for repeated range queries.

Highlights

• Range Result Cache Infrastructure: Added a dedicated range result cache to CacheManager and exposed it through CacheStrategy.
• Cache Key and Value Definitions: Introduced read/range_cache.rs to define cache keys (RangeScanCacheKey), request fingerprints (ScanRequestFingerprint), cached values (RangeScanCacheValue), and memory estimation for these structures.
• Scan Fingerprint Construction: Implemented scan fingerprint construction in scan_region.rs to identify cache-eligible reads, incorporating schema-sensitive fields like read column types and partition_expr_version.
• Unit Tests: Included comprehensive unit tests to verify cache behavior, fingerprint eligibility, and normalization.
• MergeMode Hashing: Derived the Hash trait for MergeMode to allow its participation in cache keys.

Changelog

• src/mito2/src/cache.rs
  • Imported RangeScanCacheKey and RangeScanCacheValue for the new cache.
  • Defined RANGE_RESULT_TYPE constant for metrics.
  • Added get_range_result and put_range_result methods to CacheStrategy to interact with the new cache.
  • Introduced range_result_cache field to the CacheManager struct.
  • Implemented get_range_result and put_range_result methods within CacheManager to manage the range result cache.
  • Added range_result_cache_size to CacheManagerBuilder for configuration.
  • Provided a setter range_result_cache_size for the builder.
  • Initialized the range_result_cache within CacheManagerBuilder::build.
  • Included range_result_cache in the CacheManager struct instantiation.
  • Added range_result_cache_weight function for cache memory estimation.
  • Defined RangeResultCache type alias.
  • Updated test imports to include new range cache types.
  • Added test_range_result_cache unit test to verify the new cache's functionality.
• src/mito2/src/read.rs
  • Added pub(crate) mod range_cache; to expose the new range cache module.
• src/mito2/src/read/range_cache.rs
  • Added new file range_cache.rs to define types for range scan caching.
  • Defined ScanRequestFingerprint and ScanRequestFingerprintBuilder to capture request-relevant scan options.
  • Defined RangeScanCacheKey for uniquely identifying cached range scan outputs.
  • Defined RangeScanCacheValue to store cached record batches.
  • Implemented estimated_size methods for ScanRequestFingerprint, RangeScanCacheKey, and RangeScanCacheValue for cache sizing.
  • Added unit tests to ensure correct normalization and handling of time filters in scan fingerprints.
• src/mito2/src/read/scan_region.rs
  • Imported ScanRequestFingerprint for use in scan processing.
  • Changed the time_range field in ScanInput to pub(crate) for broader access.
  • Added build_scan_fingerprint function to generate a ScanRequestFingerprint for cache-eligible scans.
  • Introduced new_scan_input helper function for testing purposes.
  • Added unit tests to validate the behavior and eligibility criteria of build_scan_fingerprint.
• src/mito2/src/region/options.rs
  • Derived the Hash trait for the MergeMode enum to allow its use in hash-based data structures like cache keys.

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[gemini-code-assist]

Code Review

This pull request introduces the necessary infrastructure for caching partition range scan results in mito2. The changes are well-structured, adding a new cache to the CacheManager, defining cache keys and values in a new range_cache module, and implementing the logic for creating scan fingerprints. The code is consistent with existing patterns and includes comprehensive unit tests. I've found one minor issue regarding memory estimation for cache keys, which could lead to the cache using slightly more memory than its configured limit. Overall, this is a solid contribution that lays the groundwork for future performance improvements.