[PERF]: remove mutex around tokenizer

[codetheweb]

Description of changes

Saves around 1,300ms when ingesting 15k documents (averaging 1000 chars each).

We spend 1.5x the tokenization time just cloning the tokens, which should be avoidable but is not included in this PR because the lifetimes get hairy and the % that tokenization takes in the total compaction time is currently fairly low.

Summarize the changes made by this PR.

• Improvements & Bug fixes
  • removes the mutex from the tokenizer, reducing overhead
  • simplifies types by removing a Box wrapper

Test plan

How are these changes tested?

Covered by existing tests.

Documentation Changes

Are all docstrings for user-facing APIs updated if required? Do we need to make documentation changes in the docs repository?

n/a

[github-actions]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)