do we need to re-encode array chunks

[d-v-b]

because we go through xarray's API for reading and writing Zarr arrays, we decompress and recompress chunks. This is necessary if we want to re-chunk the array data and / or use a different compressor. But if we don't want to do those things, then we could directly copy the bytes without decompression / compression, which would save some CPU cycles.

[emmanuelmathot]

Let's skip and do not reencode the non-measurement data.

[emmanuelmathot]

To be checked for #92