[ENH] Handle metadata deletes + fix bugs related to Updates/deletes in the metadata writer

[sanketkedia]

Description of changes

Summarize the changes made by this PR.

• Improvements & Bug fixes
  • Handles metadata deletes
  • Full text writer adds (token, freq) pair even if freq is 0. Fixes this.
  • Full text writer does not remove postings list of documents that have been deleted. Fixes this.
  • Fix for test_query_without_add

Test plan

• [x] Tests pass locally with pytest for python, yarn test for js, cargo test for rust

Documentation Changes

None

[github-actions[bot]]

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)

[sanketkedia]

Discussed offline that nothing obvious comes to mind wrt simplifying the metadata merge. At this point, ok to move on but revisit this later and assess if there are possibilities to do this