Remove outdated assertion on model support

[liam-sbhoo]

Change Description

I think this assertion is outdated.

Addition / Fix:

• TabPFNRegressor.list_available_models()
• add model support
• fix unnecessary welcoming message everytime we call fit.

I have tested it (checked from Vertex log, make sure the model specified in client is being used).

Try to be precise. You can additionally add comments to your PR, this might help the reviewer a lot.

If you used new dependencies: Did you add them to requirements.txt?

NO

Who did you ping on Mattermost to review your PR? Please ping that person again whenever you are ready for another review.

Breaking changes

If you made any breaking changes, please update the version number.
Breaking changes are totally fine, we just need to make sure to keep the users informed and the server in sync.

Does this PR break the API? If so, what is the corresponding server commit?

Does this PR break the user interface? If so, why?

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[SamuelGabriel]

LGTM

[SamuelGabriel]

looks nice, but for the one comment i left. please fix the name, then this is ready to be merged.

[liam-sbhoo]

I renamed model_path to model (although some pre-processing required, TabPFN takes both model and model_path and they meant different things).
Added some test case too.