Consider Migrating away from Nose

[gabuzi]

As mentioned in #69 (comment), the nose test library is no longer maintained, and the last release is 9 years old. It currently prevents running tests on python 3.12, which will probably become a problem in the future.

There is an actively maintained fork of nose, pynose: https://pypi.org/project/pynose/, but it is not available from conda, which will complicate building conda packages.

From a very superficial look at the code, nose is mainly used for setup, which should be available from other python unit test libraries.

[naegelejd]

Resolved by switching to pytest in #82