Fsspec: Handle all forms of range requests

[kylebarron]

obstore/obstore/python/obstore/fsspec.py

Lines 135 to 138 in 9ca85e7

	if start is None or end is None:
	raise NotImplementedError(
	"cat_file not implemented for start=None xor end=None",
	)

obstore.get_range already handles all forms of range requests; we just need to check the semantics of how fsspec considers range requests and map fsspec semantics onto our parameters