[SPARK-55024][SQL] Use REQUIRES_SINGLE_PART_NAMESPACE error for session catalog namespace validation

[cloud-fan]

What changes were proposed in this pull request?

This PR improves error consistency by using REQUIRES_SINGLE_PART_NAMESPACE instead of IDENTIFIER_TOO_MANY_NAME_PARTS when the session catalog is involved. It adds centralized namespace validation in CatalogAndIdentifier extractor: when the catalog is session catalog, validate that the namespace has exactly 1 part.

Why are the changes needed?

REQUIRES_SINGLE_PART_NAMESPACE is more precise for the namespace length error of the session catalog.

Does this PR introduce any user-facing change?

Yes, error message change

How was this patch tested?

existing tests

Was this patch authored or co-authored using generative AI tooling?

cursor 2.3.34

[github-actions]

JIRA Issue Information

=== Improvement SPARK-55024 ===
Summary: Use REQUIRES_SINGLE_PART_NAMESPACE error for session catalog namespace validation
Assignee: None
Status: Open
Affected: ["4.2.0"]

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