[Caideyipi]

Description

When LOAD falls back to tablet conversion, a model-read or conversion exception can be hidden by the earlier analysis error, and scheduler fallback reports only failed file paths. Remote dispatch also replaces a receiver rejection with a generic DISPATCH_ERROR.

• Report the current model-read or conversion failure, including the affected TsFile, in logs and client responses. Keep exception stack traces and explain conversions that return no status.
• Include each failed file's conversion status or exception in the final scheduler response, including nested insertion errors. Successful files stay out of the failure summary.
• Preserve receiver status codes, nested statuses, redirection, and retry metadata. Log rejected requests with the LOAD UUID, region, and endpoint, and handle rejections without a status explicitly.
• Add matching English and Chinese message constants and regression coverage for both file models.

Validation

• mvn spotless:apply -pl iotdb-core/datanode
• Full-reactor compilation passed for both locales: mvn -nsu test-compile -DskipTests and mvn -nsu test-compile -DskipTests -P with-zh-locale.
• 34 targeted tests passed in each locale: mvn -nsu surefire:test -pl iotdb-core/datanode -Dtest=LoadTsFileAnalyzerDiagnosticsTest,LoadFallbackHandlerTest,LoadTsFileDispatcherImplTest,LoadTsFileAnalyzerTest,LoadTsFileSchedulerTest -DforkCount=1 (also with -P with-zh-locale).
• Maven dependency analysis passed: mvn -nsu -pl iotdb-core/datanode dependency:analyze-only@check-dependencies.
• English/Chinese message-key parity, new-message placeholder/hash checks, and a scan for added user-facing English literals.

This PR has:

• been self-reviewed.
• added unit tests or modified existing tests to cover the changed error paths.

Key changed classes: LoadTsFileAnalyzer, LoadFallbackHandler, LoadTsFileDispatcherImpl.