Combine multiple small fetches

[cmdcolin]

Currently, jbrowse uses http-range-fetcher to 'aggregate all the fetches that have occurred in the last 100ms'

this can be potentially** problematic though

a) it requires any use of cram-js to use http-range-fetcher or similar workaround to get reasonable performance
b) if you get into a weird scenario where you aren't caching requests right, it can get into a very slow mode (xref GMOD/jbrowse-components#4555)

it might be good to bundle multiple requests together automatically if possible

[cmdcolin]

similar issue in bbi-js GMOD/bbi-js#55