Make tensortrax optional

[adtzlr]

like JAX

closes #893

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 97.28%. Comparing base (29571c1) to head (298d0d8).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/felupe/__init__.py	66.66%	2 Missing ⚠️
src/felupe/constitution/__init__.py	80.00%	2 Missing ⚠️
src/felupe/constitution/jax/__init__.py	80.00%	2 Missing ⚠️
src/felupe/constitution/tensortrax/__init__.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #894   +/-   ##
=======================================
  Coverage   97.28%   97.28%           
=======================================
  Files         171      171           
  Lines        6140     6149    +9     
=======================================
+ Hits         5973     5982    +9     
  Misses        167      167           

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