refactor(index): pass resolved bucket mode to index manifests - #494

Purpose

Linked issue: part of #493

IndexManifestFile and IndexManifestFileHandler received the configured bucket option and
treated -1 as BUCKET_UNAWARE when choosing how to combine deletion vector index entries. A
primary-key table with dynamic buckets also has bucket = -1, but keeps one deletion vector index
per (partition, bucket), so it must use the bucketed combiner, as Java does for
BucketMode.HASH_DYNAMIC.

This change passes the resolved BucketMode (ResolveBucketMode(options.GetBucket(), schema))
everywhere an IndexManifestFile is created, and only uses the global deletion vector combiner
for BUCKET_UNAWARE. That combiner merges entries by index file name and uses data file names
only to reject a data file covered by more than one deletion vector.

There is no behavior change for tables that can be written today: dynamic bucket primary-key
tables are still rejected by the writer. This is the first step of #493; batch reads of those
tables follow in a separate PR.

Tests

• IndexManifestFileHandlerTest: existing cases now pass an explicit BucketMode; added
  DynamicBucketDvUsesBucketedCombiner, which goes through IndexManifestFile::Create() and
  WriteIndexFiles() so the stored bucket mode is exercised end to end. It checks that a new
  deletion vector index of a HASH_DYNAMIC table replaces the previous one of the same
  (partition, bucket) and leaves other buckets untouched, while a separately created
  BUCKET_UNAWARE manifest rejects the same delta with
  Trying to add a second deletion vector for data file data-0.orc.
• IndexFileHandlerTest resolves the bucket mode with ResolveBucketMode() from the table
  schema, the same way production callers do.
• Updated callers in CommitScannerTest, ExpireSnapshotsTest, FileSystemWriteRestoreTest
  and OrphanFilesCleanerTest.

Verified on Ubuntu 24.04 (aarch64), GCC 13, Debug: the affected suites pass (40 tests) and the
full paimon-core-test passes (2536 tests).

API and Format

No public API change (only internal headers under src/). No storage format or protocol change.

Documentation

No.

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