numpy 1.26.4 dependency

[kkappler]

To make this package easy to include with others it would be nice to relax the restriction on numpy==1.26 version in the environment.yaml.

I think this restriction originally came from SimPEG (and further still from one of it's dependencies), but couldn't find any threads on this -- perhaps it is no longer required ... (I have had some success at least using geoana with numpy 2.3) ... although it seems to matter which python version i use, i.e. 3.9 gives errors in discretize, but 3.10, 3.11 seem fine.

TODO:

• After PR Features #77 is merged, fork main to fix_issue_84 and edit the environment.yaml to remove the 1.26 pin and see if tests pass