Miscellaneous housekeeping improvements

[aarmey]

Apologies that this does not involve just one change. This resolves some various minor inconsistencies, deprecations, and performance issues:

• In both the PLSR and HALS implementations, this reduces indexing which improves performance, particularly for Jax and TensorFlow
• Some methods were not being exported or had missing arguments in their docstrings
• Most backends provide the np.lstsq interface, so all four return values are passed on now
• As suggested in #448, this adds pytest-randomly. This sets the random seeds of the default random generators and reports it in output. I've found this is very helpful when dealing with inconsistent errors.
• Python v3.8 is now EOL, so I removed some code ensuring its support. The default Python version is now 3.11 in testing.

I will further annotate each of the changes so that this is simpler to review.

[codecov[bot]]

Codecov Report

Merging #513 (b5161a7) into main (94c2ff2) will increase coverage by 0.07%. Report is 3 commits behind head on main. The diff coverage is 90.62%.

@@            Coverage Diff             @@
##             main     #513      +/-   ##
==========================================
+ Coverage   86.71%   86.78%   +0.07%     
==========================================
  Files         120      118       -2     
  Lines        7535     7515      -20     
==========================================
- Hits         6534     6522      -12     
+ Misses       1001      993       -8     

Files Changed	Coverage Δ
tensorly/__init__.py	100.00% <ø> (ø)
tensorly/utils/__init__.py	100.00% <ø> (ø)
tensorly/tenalg/proximal.py	67.68% <71.42%> (+0.23%)	:arrow_up:
tensorly/backend/core.py	67.67% <80.00%> (-0.01%)	:arrow_down:
tensorly/backend/__init__.py	89.83% <100.00%> (ø)
tensorly/base.py	95.83% <100.00%> (ø)
tensorly/decomposition/_cp.py	83.71% <100.00%> (-0.11%)	:arrow_down:
tensorly/decomposition/_tr.py	85.24% <100.00%> (ø)
tensorly/decomposition/tests/test_cmtf_als.py	100.00% <100.00%> (ø)
tensorly/metrics/entropy.py	86.36% <100.00%> (-0.60%)	:arrow_down:
... and 4 more

... and 1 file with indirect coverage changes

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