[ENH]: Propagate cancellations to NAC queue (#5129)

## Description of changes

_Summarize the changes made by this PR._

- Improvements & Bug fixes
- When a future running a NAC request gets dropped, it "removes" its
priority from the pending request if it hasn't been sent out to object
storage yet.
- The priority data structure for in-flight requests has been updated
from a binary value of priorities to a set of counters, denoting how
many tasks requested each priority level.
- New functionality
- Ideally, the above changes should make it such that high priority NAC
requests get lowered in priority when the calling requests are
cancelled/timed out.

## Test plan

_How are these changes tested?_

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

## Migration plan
N/A

## Observability plan
It would be a good idea to add a metric that tracks the number of total
waiters on the NAC layer.

## Documentation Changes

_Are all docstrings for user-facing APIs updated if required? Do we need
to make documentation changes in the [docs
section](https://github.com/chroma-core/chroma/tree/main/docs/docs.trychroma.com)?_