Reject a DataSourceConfig with no uri or format in DataFusionEngine

[pankajastro]

Follow-up per review feedback on #73273.

LLMSQLOperator, DataFusionToolset, and AnalyticsOperator hand DataFusionEngine.register_datasource whatever DataSourceConfig the caller supplies, unlike LLMSchemaCompareOperator which checks the connection kind first. A plain-database-table config reaching any of them failed deep inside credential resolution with a confusing Unknown connection type error instead of a clear message. register_datasource now rejects that shape immediately.

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Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Sonnet 5)

Generated-by: Claude Code (Sonnet 5) following the guidelines

[potiuk]

The guard is correct and lands exactly where it should: storage_type is None on a non-table-provider config is, by DataSourceConfig.__post_init__'s invariants, exactly the "neither uri nor format" shape, so the check turns the misleading Unknown connection type failure from _get_credentials into a clear error before any connection lookup, and the new test fails without it.

I traced the three pass-through callers (LLMSQLOperator, DataFusionToolset, AnalyticsOperator) and every DataSourceConfig(...) in the common-ai / common-sql tests; none hands a plain-table config to a real engine, and the existing docs already describe uri/format as required for those consumers, so nothing else changes.

Smaller observations

• The commit carries a Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> trailer. AGENTS.md ("Commits and PRs") says "Never list an agent as a commit co-author"; the Generated-by: line in the description is the sanctioned disclosure. I'll drop the trailer from the squash message at merge time.
• For LLMSchemaCompareOperator, a plain-table config whose conn_id is mistyped now reports "has no uri or format" instead of "conn_id isn't defined" (because _is_dbapi_connection swallows the not-found error and falls through to DataFusion). Probably the right layering; just noting the message no longer points at the real cause in that one case.

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