builder/stream_builder: validate UC three-part table name format in validate()

[Dev-X25874]

What changes are proposed in this pull request?

WHAT: StreamBuilder::validate() now checks that the table name follows the
required catalog.schema.table format, returning ZerobusError::InvalidTableName
immediately if it does not.

WHY: validate() previously only checked that the table name was non-empty.
A malformed name like "mytable" or "schema.table" would pass validate() and
build(), only to fail later inside the async OAuth token fetch — far from the
misconfigured builder. The three-part invariant was already enforced in
DefaultTokenFactory::parse_table_name; this PR moves that check to the earliest
possible point so the error fires synchronously, before any I/O occurs.

How is this tested?

Three unit tests added to the existing #[cfg(test)] block in stream_builder.rs:

• validate_rejects_single_part_table_name
• validate_rejects_two_part_table_name
• validate_rejects_table_name_with_empty_part

All three fail on the original code and pass after the fix.

[teodordelibasic-db]

LGTM, thanks for contributing, let's only do this when testing feature is off.

[teodordelibasic-db]

We should guard this block with #[cfg(not(feature = "testing"))] because we use non-three-part table names when testing.

[Dev-X25874]

@teodordelibasic-db Done, guarded the block with #[cfg(not(feature = "testing"))] in the latest commit.

[teodordelibasic-db]

LGTM, you just need to rebase to newest main.

[Dev-X25874]

@teodordelibasic-db Done, rebased onto latest main. Ready for another look!

[teodordelibasic-db]

Ah so we are hitting an issue where CI is broken for external contributions from forks because of the need to fetch a JFrog token to access the proxy registry. I have asked internally if there is an established solution for this.