Add doc for chromsizes grid overlay (higlass#187)

fix: Resolve Jupyter server tile sources in combined tracks (higlass#186

)

feat(widget): Batch tile requests within an animation frame (higlass#181

)

* feat(widget): Batch tile requests within an animation frame

HiGlass's built-in data fetching logic is designed to optimize API calls
by consolidating requests based on time, ID, and server. Our custom
Jupyter data fetcher doesn't include these optimizations.

This PR introduces a `consolidator` helper, which performs a much simpler
form of batching. Since we assume a single server, this function only
batches tile requests that occur within the same animation frame and
submits them together. This helps reduce the number of comms calls and
deduplicates requests efficiently.

Initial testing suggests it feels quite responsive!

* Add `MAX_TILES_PER_REQUEST` const

* Use `Promise.withResolvers`

* Remove chunkIterable for now

feat: Add stub `higlass.server` with deprecation warnings (higlass#178)