Optimize load partition routing

[Caideyipi]

Summary

• Avoid borrowing a ConfigNode client when load data partition can be served from cache.
• Reduce duplicated partition-slot routing work for single TsFile and chunk-data load paths.
• Replace stream-heavy partition query result assembly with pre-sized loops.

Tests

• mvn -DskipTests spotless:check -pl iotdb-core/datanode
• mvn -DskipTests -Dcheckstyle.skip=true -pl iotdb-core/datanode compile (fails locally in unrelated generated-source/cache state: missing IFill/Accumulator/ComparatorChain and QueryModificationLoader signature mismatch; touched files are not reported)