Array API compatibility for pytorch and jax

[faymanns]

This pull request implements moves splinebox to the array API standard so it can accept torch and jax arrays in the future. This will allow using autodiff.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.50549% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.86%. Comparing base (20e67e5) to head (f475e1e).

Files with missing lines	Patch %	Lines
src/splinebox/basis_functions.py	94.47%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #91      +/-   ##
==========================================
- Coverage   96.38%   95.86%   -0.52%     
==========================================
  Files           4        4              
  Lines        1271     1379     +108     
==========================================
+ Hits         1225     1322      +97     
- Misses         46       57      +11     

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