Fix oversized Load TsFile piece dispatch

[Caideyipi]

Summary

Load TsFile dispatch could send a serialized LoadTsFilePieceNode larger than dn_thrift_max_frame_size, causing the receiver to reject the Thrift frame.

This change:

• slices oversized piece RPC payloads below the configured Thrift frame limit;
• adds slice metadata to TTsFilePieceReq and reassembles slices in order on the DataNode;
• keeps small requests on the existing wire format;
• integrates partial-slice cleanup, rollback, and EXECUTE validation.

Verification

• LoadTsFileDispatcherImplTest: 4 tests passed
• LoadTsFilePieceNodeAssemblerTest: 4 tests passed
• DataNode Checkstyle/Spotless passed
• DataNode compile passed with -Pwith-zh-locale

The sender and receiver DataNodes should be upgraded together because older receivers do not understand the new slice metadata.