[FEATURE] Enables offline /score for embedding models

[gmarinho2]

Enables LLM.score() for all embedding models. The request_id consists of the request_ids of each embedding in the pair, separated by "_". The prompt_token_ids are the concatenation of all the token ids, in order and separated by the padding token when it is available. This PR is the first of two for completing the issue. The second PR will implement the same feature in the OpenAI API.

Issue: [Feature]: Enable /score endpoint for all embedding models (1/2)

[github-actions]

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[joerunde]

@maxdebayser @gmarinho2 This looks like it only touches the offline entrypoint, but the PR title mentions /score endpoint which I had assumed meant the online REST interface.

It's not 100% clear to me from the linked issue either what was intended- is there more work planned to support the online interface or are we only aiming for offline?

[maxdebayser]

@joerunde, we're aiming for both. @gmarinho2 started with the offline API first.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @gmarinho2.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[maxdebayser]

I've left some suggestions, but it looks good to me. I think we can open this as a PR now.

[DarkLight1337]

Some initial comments.

I also suggest splitting out the logic for scoring and general embedding models into separate functions.