Skip bitshuffle as a dep on windows

[MridulS]

Make bitshuffle an optional dep as it doesn't have wheels/conda packages for windows.

[SimonHeybrock]

Does this mean parts of the functionality will be broken on Windows, or is it somehow falling back to not use bitshuffle?

[MridulS]

Yes it falls back on gzip

essnmx/src/ess/nmx/nexus.py

Lines 76 to 80 in 515849b

	UserWarning(
	"Could not find the bitshuffle.h5 module from bitshuffle package. "
	"The bitshuffle package is not installed properly. "
	"Trying with gzip compression instead..."
	),