Address Jax/Jaxlib v0.4.x compatibility, incorporate CircleCI testing workflows, incorporate versioneer.

[thomaspinder]

This PR:

• Fixes the typing in GPJax to be compatible with Jax/Jaxlib v0.4.1.
• Incorporates CircleCI workflows to run tests.
• Incorporates versioneer to determine the library version from git tags.

Pull request type

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• [ x] Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

We currently:

• Type an array using DeviceArray. As of Jax v0.4.1, DeviceArray has been replaced by Array.
• Use standard GitHub workflows.
• Use a static library version defined in gpjax/__init__.py.

Issue Number: #156

New behaviour

• Migrate to jax.Array's for compatibility for JAX v0.4.x.
• Incorporate CircleCI workflows for testing. Might extend this to build docs in future.
• Incorporate versioneer that automatically retrieves the package version in gpjax/__init__.py from git tags.

[codecov-commenter]

Codecov Report

Merging #164 (5aac7a0) into master (e0439b3) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
- Coverage   96.87%   96.76%   -0.11%     
==========================================
  Files          15       15              
  Lines        1407     1424      +17     
==========================================
+ Hits         1363     1378      +15     
- Misses         44       46       +2     

Flag	Coverage Δ
unittests	96.76% <100.00%> (-0.11%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
gpjax/kernels.py	91.42% <ø> (-0.07%)	⬇️
gpjax/utils.py	100.00% <100.00%> (ø)
gpjax/config.py	96.66% <0.00%> (-3.34%)	⬇️
gpjax/gps.py	100.00% <0.00%> (ø)
gpjax/natural_gradients.py	100.00% <0.00%> (ø)

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[daniel-dodd]

@thomaspinder nice PR. Left a few comments. Please in future can you fully state all features that have been added in the description, as we have not only bumped JAX, we have also integrated CircleCI and versioneer. (I have added these to the description).

One suggestion (nice have, but not requirement for this PR) I have is - do we really want all that (same) versioneer code in all repositories? It might be quite annoying to maintain?

[thomaspinder]

@thomaspinder nice PR. Left a few comments. Please in future can you fully state all features that have been added in the description, as we have not only bumped JAX, we have also integrated CircleCI and versioneer. (I have added these to the description).

One suggestion (nice have, but not requirement for this PR) I have is - do we really want all that (same) versioneer code in all repositories? It might be quite annoying to maintain?

Apologies - I thought by merging others PRs into this one that comments would come across too.

The versioneer code is autogenerated. I don't see a clean way to "share" it across packages so I'm personally fine with it as is.