preload and cache whole time series

## Use Case

It can be slow to play through time. AGAVE currently only loads one timestep at a time.

## Solution

for small-enough data, we could load a whole time series and cache rather than re-fetch from source file every time. We could also implement a agave-local disk cache for all file formats, for highly accelerated read times. it could dump the data to zarr or some even more basic format for fast loading.