[XiaoHongbo-Hope]

Summary

• Keep one local-cache size budget while protecting metadata and global-index blocks in a separate LRU. Either priority class can borrow unused capacity.
• Add local-cache.high-priority-pool-ratio (default 0.25; 0 restores a single LRU). Apply the policy to memory and disk caches, including disk recovery, without changing the on-disk block format.
• Cover eviction, disabled priority, disk restart, configuration, and real reader behavior.

Validation

• cargo fmt --all -- --check: passed
• cargo test -p paimon --lib cache: 129 passed (storage-fs,storage-memory)
• cargo clippy -p paimon --lib --tests: passed with two pre-existing storage.rs warnings suppressed under this feature set
• Full lib run: 4,322 passed, 1 failed, 7 ignored. The failure was empty_target_does_not_bypass_mutation_authorization in a parallel run; it passed when rerun alone. No local-cache code is on that test path.

No production OSS/QPS benchmark was run. This PR targets current main; the unmerged cross-process shared cache in #1175 will need a separate integration with the same policy.

[JingsongLi]

+1