perf(readutil): preserve early filtering across fallback paths

[XuPeng-SH]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #25588

What this PR does / why we need it:

This PR preserves early filtering across three safe but expensive fallback paths:

• represents OR-ed primary-key filters as atomic specs and heap-merges partition-state iterators, including tombstones, with overlap deduplication;
• replaces the PREFIX_IN > 4 pass-through with an immutable, sorted prefix index and eagerly builds the regular IN lookup;
• preserves compilable conjuncts in top-level and nested AND filters while keeping OR compilation all-or-nothing.

It also exposes disjunct/key counts for observability and adds BVT coverage for committed partition-state rows, persisted mixed filters, large compound-PK prefix lists, NULLs/duplicates, overlapping OR branches, and workspace rows.

Testing

• owning-package tests: readutil, logtailreplay, and disttae
• focused race tests (-count=10) and stress tests (-count=100)
• full owning-package race tests
• go vet and go build for modified packages
• make build
• local mo-tester BVT against the branch-built server: 23/23 passed (100%)
• benchmark with 8,192 encoded keys and 1,024 prefixes: about 0.37-0.48 ms/op, 0 alloc/op

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[LeftHandCold]

Reviewed the OR union iterator, tombstone path, immutable IN/PREFIX_IN lookup, partial-AND compilation, fallback semantics, iterator ownership, and observability changes. The subset compilation remains fail-open/safe because residual expressions still evaluate the full predicate; OR remains all-or-nothing. Child iterators are closed on all owning paths, prefix/disjunct state is bounded by filter input, and the new immutable lookup is race-safe. Owning-package tests, focused race tests (10x), and a 10,000-case PREFIX_IN differential check all passed. No blocking issues found.

[gouhongshen]

Codex automated review

No blocking or non-blocking correctness findings in b7fa79d relative to origin/main. Focused Go tests could not run because this checkout lacks the required MatrixOne CGo library (cgo/libmo.dylib).