Update test matrix and add scheduled tests

[matt-graham]

Updates test matrix to run tests across all supported Python versions (currently Python 3.8 – 3.12) and operating systems. Also adds weekly scheduled test runs to resolve #208.

Given this makes the test matrix quite large (15 combinations of OS and Python version), and Python 3.8 and Python 3.9 are both out of the recommended support window of both SPEC0 and NEP29, I would also recommend we consider dropping Python 3.8 and Python 3.9 support (in a separate PR).

EDIT: Appears that there are not Windows wheels available for healpy / pyssht and we're getting a segfault somewhere when using MacOS / Python 3.9+ so reverting to only testing on Ubuntu + (MacOS, Python 3.8) for now.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.07%. Comparing base (57c07e5) to head (b6228fa).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #210   +/-   ##
=======================================
  Coverage   96.07%   96.07%           
=======================================
  Files          31       31           
  Lines        3567     3567           
=======================================
  Hits         3427     3427           
  Misses        140      140           

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[matt-graham]

I've merged in main to resolve conflicts from some files also edited in #233 (mainly some manual edits to make docstrings raw here to avoid issues on newer Python versions that Ruff also flagged and fixed). I've also added a path filter to the pull-request trigger here to only run tests workflow when we are updating files which could lead to changes in test behaviour, which should prevent needing to run tests when for example just updating Markdown files or metadata files like all-contributorsrc.

[CosmoMatt]

Weird that we're running into issues with the actions MacOS workers, but we can address this later. In any case, great to set up testing across a variety of architectures, and importantly the nightly tests!