feat(core): complete file index write lifecycle

[zjw1111]

Purpose

Linked issue: #173

Follow up the file-index write support from #210 and complete its writer and file lifecycle behavior:

• delete DataFileMeta extra files during snapshot expiration, append and merge-tree abort/cleanup, commit abort, and orphan-file cleanup
• reject writes after close before mutating file-index state
• keep changelog writers from creating file indexes
• expose and reuse the lookup file suffix constant
• cover multiple index types on one column, external-index cleanup, snapshot expiration, rolling/compaction abort, and orphan cleanup

Tests

• cmake --build build --target paimon-core-test paimon-clean-inte-test paimon-read-inte-with-index-test -j 64
• 166 focused core tests from the affected suites
• 3 CleanInteTest orphan-cleanup cases
• 4 ReadInteWithIndexTest bitmap-index-with-deletion-vector cases
• pre-commit run on all changed files
• git diff --check upstream/main...HEAD

API and Format

No public include-directory API, storage-format, or protocol changes.

Documentation

No user-facing documentation change is required.

Generative AI tooling

Generated-by: Codex (GPT-5)

[lxy-9602]

+1