[core] Unify manifest entry caching by physical block

[leaves12138]

Purpose

Unify the whole-manifest entry cache and the compressed Avro block cache used by sidecar-selected reads into one decoded-entry cache at physical block granularity.

This draft is based on current master, after #9897 and #9908. It contains only the Java cache changes and their tests/documentation, not the deferred Python writer integration from #9743.

Changes

• Change ManifestEntryCache to ObjectsCache<BlockKey, ManifestEntry, ManifestEntrySegments>, keyed by manifest path, offset and encoded block length.
• Let full reads and sidecar-selected reads reuse complete, unfiltered decoded blocks. Apply each query's predicates and converter after retrieving the block.
• Remove the separate compressed-block cache from SelectedBlockInput; keep the independent sidecar metadata-byte cache unchanged.
• Cache a complete physical block directory after reaching EOF or selecting all blocks, so a subsequent full read can find previously cached entries.
• Preserve physical entry order and ADD/DELETE semantics. Account for decoded buffers and lookup metadata, and replay an oversized block without retaining a partial cache entry or re-reading the file.
• Add coverage for full/selected cache reuse, distinct keys, filters, ordering, failure paths, memory limits and concurrent queries.

Scope

No manifest/sidecar on-disk format or writer behavior changes. The cache.manifest-sidecar.max-memory option and its default are unchanged. This is a draft for review of the cache design and implementation; production performance validation is not claimed here.

Validation

• Formatting and git diff --check passed.
• Targeted Maven reactor tests passed on the rebased branch: core 369 tests (1 skipped), common 2 tests, with no failures or errors.
• Command: mvn -pl paimon-core -am -DwildcardSuites=none -Dtest=Manifest*Test,ObjectsCacheTest,SegmentsCacheTest,DataPagedOutputSerializerTest,DataEvolutionBatchScanTest,CoreOptionsTest -DfailIfNoTests=false -Dsurefire.failIfNoSpecifiedTests=false test.