[AMORO-4345][Iceberg] Fix catalog table listing isolation

[csurong]

Why are the changes needed?

Close #4345.

When mixed-format discovery encounters an Iceberg table whose metadata file is missing, table loading aborts the entire namespace listing. The failure is then incorrectly reported as a missing database, which hides healthy tables and obscures the actual cause.

Brief change log

• Skip tables that cannot be loaded because their metadata is missing or the table was concurrently removed, while recording a warning.
• Convert only NoSuchNamespaceException to NoSuchDatabaseException and preserve other failures.
• Add regression tests for missing metadata, concurrent table removal, missing namespaces, and unexpected failures.

How was this patch tested?

• Add test cases that check the changes thoroughly including negative and positive cases if possible
• Add screenshots for manual tests if appropriate
• Run test locally before making a pull request

./mvnw -q -pl amoro-format-iceberg -am test
./mvnw -q -pl amoro-format-iceberg -am validate

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[xxubai]

LGTM