[catalog] Preserve exception cause when rethrowing catalog exceptions

[XuQianJin-Stars]

Several places in the catalog code rethrow caught exceptions by passing only getMessage() to the new exception, which drops the original stack trace and cause. This makes diagnosing failures harder because the root cause is lost.

Preserve the cause by passing the original Throwable as the second argument to the exception constructor in:

• FlinkCatalog (createTable: lake-table-already-exist and invalid-table branches; alterTable: invalid-table branch)
• PaimonLakeCatalog (AddColumn ColumnAlready/NotExistException branch)
• CoordinatorService (UncheckedIOException and generic validate branches when wrapping into InvalidTableException)

No behavior change other than richer exception chaining.

Purpose

Linked issue: none (minor code cleanup, no GitHub issue filed)

Several places in the catalog code rethrow caught exceptions by passing only
getMessage() to the new exception, which drops the original stack trace and
cause. This makes diagnosing failures harder because the root cause is lost
from the logs.

This PR preserves the cause by passing the original Throwable as the second
argument to the exception constructor, so that exception chaining is kept
intact and the root cause is visible in logs.

Brief change log

• FlinkCatalog#createTable: preserve cause in the lake-table-already-exist
  branch (new CatalogException(t.getMessage(), t)) and the invalid-table
  branch (new InvalidTableException(t.getMessage(), t)).
• FlinkCatalog#alterTable: preserve cause in the invalid-table branch
  (new InvalidTableException(t.getMessage(), t)).
• PaimonLakeCatalog: preserve cause for the
  ColumnAlreadyExistException | ColumnNotExistException branch in
  AddColumn handling
  (new InvalidAlterTableException(e.getMessage(), e)).
• CoordinatorService: preserve cause when wrapping UncheckedIOException
  and generic validation errors into InvalidTableException.

Tests

No new tests are added. This is a trivial rework that only changes the
exception-construction call to additionally pass the original Throwable
as the cause. Behavior of existing tests is unaffected.

API and Format

No API or storage format changes. The exception types thrown remain the
same; only the cause field of the thrown exceptions is now populated.

Documentation

No documentation changes. This is an internal cleanup without any
user-facing behavior change.

[Copilot]

Pull request overview

This PR improves debuggability of catalog-related failures by preserving the original exception cause (and therefore stack trace) when rethrowing/wrapping exceptions in several catalog and coordinator code paths. This keeps exception chaining intact without changing the exception types thrown.

Changes:

• Preserve cause when wrapping parsing/validation exceptions into InvalidTableException in CoordinatorService#createTable.
• Preserve cause when wrapping Paimon catalog column exceptions into InvalidAlterTableException in PaimonLakeCatalog#alterTable.
• Preserve cause when rethrowing lake-table-already-exist and invalid-table cases in FlinkCatalog#createTable and FlinkCatalog#alterTable.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
fluss-server/src/main/java/org/apache/fluss/server/coordinator/CoordinatorService.java	Adds the caught exception as the cause when wrapping parse/validation failures into InvalidTableException.
fluss-lake/fluss-lake-paimon/src/main/java/org/apache/fluss/lake/paimon/PaimonLakeCatalog.java	Preserves the original Paimon exception as the cause when rethrowing as InvalidAlterTableException.
fluss-flink/fluss-flink-common/src/main/java/org/apache/fluss/flink/catalog/FlinkCatalog.java	Preserves the original throwable as the cause when rethrowing CatalogException/InvalidTableException in specific branches.

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[luoyuxia]

+1