refactor: TableReader

[sjrl]

Related Issues

• Addresses part of Support of longer tables in TableReader #1723

Proposed Changes:

I refactored the TableReader class to make it easier to address issue #1723, which will be solved by either supporting a new table encoder or by implementing a sliding window approach. There will be a follow-up PR to finish solving issue #1723.

• Refactoring of TableReader class to work similarly to the EmbeddingRetriever class where we can more easily swap out different table encoders.
• Updated the tests to explicitly test the TapasForScoredQA architecture.
• Updated the tests to use a smaller tapas model where possible to increase the speed of the tests.

How did you test it?

The API for loading a TableReader has not changed so existing unit and integration tests all pass.

Notes for the reviewer

@bogdankostic I'd appreciate a review of this refactor since I'm changing your original implementation. Please let me know if you have any comments or concerns.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added tests that demonstrate the correct behavior of the change
• I've used the conventional commit convention for my PR title
• I documented my code
• I ran pre-commit hooks and fixed any issue

[julian-risch]

The auto-assignment of reviewers added me here but I agree with Sebastian that Bogdan is the best person to review this PR. Therefore, I unassigned myself. Just let me know if you need a second opinion on the PR. My highlight of this PR are the smaller tapas models in the tests. Thanks for speeding them up! 👍

[bogdankostic]

Thanks for this PR, looks very good already :) I only left two minor suggestions

[bogdankostic]

LGTM, just one very small nitpick :)