Load: Fix active load reliability issues

[Caideyipi]

Description

Active load handoff

• Transfer each TsFile and its resource/mods files through a unique directory, publish the TsFile last, and clean partial output on failure.
• Keep source files until the whole handoff succeeds and isolate same-name file groups from one another.

Scanner and loader lifecycle

• Deduplicate scanner candidates derived from TsFiles and companion files.
• Prevent internal attribute/transfer directories from being inferred as table databases.
• Clear stale pending state across loader restarts and clean empty transfer directories after processing.

Load resource cleanup

• Release cached LOAD memory when split/routing exits early.
• Retry deletion of the TsFile and each companion independently so one failure does not skip the remaining cleanup.

Test coverage

• Datanode load unit-test suite: 41 tests passed.
• Final focused regression suite: 15 tests passed.
• Spotless check, Checkstyle, and git diff --check passed.

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This PR has:

• been self-reviewed.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage.

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Key changed/added classes (or packages if there are too many classes) in this PR

• LoadSingleTsFileNode and LoadTsFileScheduler
• ActiveLoadDirScanner, ActiveLoadPendingQueue, and ActiveLoadTsFileLoader
• LoadUtil