Query timeouts and unreachable-database errors were being caught by the
broad SupersetException handler in CreateDatasetCommand and coerced into
a 422 DatasetInvalidError, indistinguishable from a bad table name. Let
SupersetTimeoutException and SupersetDBAPIConnectionError/OperationalError/
DatabaseError propagate so they reach the client with their own status via
the existing SupersetException error handler.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>