Numpyro sampler option, documentation, land/sea map fix, save trace fix

[brendan-m-murphy]

This branch adds the option to use Numpyro's NUTS sampler in place of the pymc NUTS sampler. This seems to be 7-10x faster. This addresses issue #17 and the ACRG project issue #30, although profiling needs to be done to assess the speed improvements.

It also adds some documentation by expanding the readme file and adding a short overview (https://github.com/openghg/openghg_inversions/tree/numpyro-fixed-outer-regions)

There are fixes to two other issues as well:

• Issue #99 and issue #56 are addressed by adding the land/sea split file to the repository and changing how this file is searched for. (Issue #99 is only partially addressed, because that asks for the option to specify a path to this file.)
• The save_trace option was removed in a previous PR; it is restored in this PR.
• NaN values are dropped before data is passed to pymc, partly addressing issue #97. (Still need to log warnings about missing data.)
• The option to compute the min model error on the fly was added. Also, min model error is saved in the attributes of the inversion output.

Also, a link to the DOI associated with releases was added to the readme file, and a test was added for the bucket/weighted basis function.

[brendan-m-murphy]

@joe-pitt reports: error using weighted basis with fixed outer regions:

[Yesterday 21:23] Joe Pitt File "/user/home/zh21490/openghg_inversions/openghg_inversions/basis/_functions.py", line 201, in fixed_outer_regions_basis

basis.loc[loc_dict] = (inner_region + 5).squeeze().values

[Yesterday 21:24] Joe Pitt ValueError: could not broadcast input array from shape (183,128) into shape (182,127)