fix: Handle qualified tableau datasources more gracefully

[alanmcruickshank]

Summary of Changes

When unpacking tableau datasources, if a table reference had more than two parts (i.e. database.schema.table rather than just table or schema.table) this would raise a KeyError during unpacking and the script would stop abruptly.

This fix adds handling code for greater degrees of qualification and also a graceful path for dbapis which have potentially very long qualification options (e.g. foo.bar.baz.db.schema.table). I haven't accounted for anything more specific that something that will work for now, although that would be something that could be built on at a later date. This solution solves for the most common use case where the database may be qualified in the table reference.

Tests

No tests added as I don't believe there is an existing test which could be extended to cover this case. I'm still new to the codebase to any pointers on a sensible test to add would be excellent and I'm happy to implement one.

Documentation

No documentation added - I believe this should be the expected behaviour.

CheckList

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[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[alanmcruickshank]

@feng-tao - anything I need to do to help this through the review process?

[feng-tao]

thanks @alanmcruickshank ! looks good and merge it now.