LOAD TsFile: use the Pair the resolver takes and cover the HA cases

[luoluoyuyu]

Description

The router and the resolver each wrapped a (device, time partition) pair into a private record only to unwrap it again on the way in or out. Pair already carries the value equality the deduplication maps need, so keep the pair itself and drop both SlotKey records, the record and its conversion.

Cover the two cluster cases the consensus LOAD path has to survive:

• a LOAD that runs while one DataNode is down: restarting that DataNode must replay the LOAD commands it missed and serve the loaded file.
• a LOAD whose region is migrated mid-flight: the LOAD has to follow the refreshed route or fall back to the tablet path, but every point of the file must be imported and the migration must finish.

---

This PR has:

• been self-reviewed.
  • concurrent read
  • concurrent write
  • concurrent read and write
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods.
• added or updated version, license, or notice information
• added comments explaining the "why" and the intent of the code wherever would not be obvious
  for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold
  for code coverage.
• added integration tests.
• been tested in a test IoTDB cluster.

---

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