WASMFS fetch backend should support range queries

[JoeOsborn]

This is a feature request, not a bug, so sorry if this is the wrong channel.

The old createLazyFile synchronous XHR code implemented range queries to only obtain portions of large files over the network instead of doing one massive read into memory; its internal LazyUint8Array stored chunks of files and proxied reads into the chunks, making new network requests to fill the chunks as needed. It would be great if the new WASMFS fetch backend could have configurable min and max network request sizes and, if I may be so bold, memory occupancy limits with LRU deletion of chunks.

If someone were to implement this, would a good start be to copy and modify the fetch backend, merging in relevant parts of the jsfile backend modified so that a file is a bunch of chunks instead of a single typed array?