[core] Search fresh level-0 files in PK vector search full modes

[LuciferYang]

Purpose

close #9894

PrimaryKeyVectorRead handed the bucket search only the files PrimaryKeyIndexSourcePolicy.shouldRead accepts (complete COMPACT level>0 outputs), so Level-0 APPEND files, the rows written since the last compaction, were omitted by every search mode, including full and detail, which are documented to exact-scan unindexed data files. This passes all data files of the split (filesToSearch) to the bucket search instead. The exact fallback then covers the files the ANN segments do not, FAST keeps ignoring them, and the ANN state builder (PkVectorBucketIndexState.fromActiveDataFiles) still applies the compact-file policy internally, so the ANN segment state is unchanged and only the exact-scan file set widens.

Note: on a first-row merge-engine table with deletion vectors disabled, exact-scanning uncompacted files in full/detail mode can surface a superseded row version, because the exact scan returns physical rows without a merge-on-read dedup. This is a pre-existing property of the exact scan (it already applied to superseded versions promoted into compacted files); including level-0 files makes it more frequent rather than introducing it. The deletion-vector-enabled path is unaffected, since superseded rows are deletion-vector-marked and excluded. Tracked in #9895.

Tests

The synchronous write harness compacts eagerly and cannot hold a stable level-0 window, so the coverage pins the two halves of the chain separately:

• PrimaryKeyVectorReadTest#testFilesToSearchIncludesAppendLevel0Files: filesToSearch returns an APPEND level-0 file that shouldRead rejects. Against the old filtered list the append file is absent, so this fails.
• PrimaryKeyVectorReadTest#testFullModeBucketSearchExactScansAppendLevel0Files: the bucket search exact-scans that level-0 file in full mode and returns it, while FAST still skips it.