Support multi-dimensional output for CP regression

[merajhashemi]

This pr resolves #51 (CP only).

[codecov]

Codecov Report

Merging #252 (2727188) into main (e5dd284) will decrease coverage by 3.37%.
The diff coverage is 100.00%.

❗ Current head 2727188 differs from pull request most recent head 2dcee40. Consider uploading reports for the commit 2dcee40 to get more accurate results

@@            Coverage Diff             @@
##             main     #252      +/-   ##
==========================================
- Coverage   86.86%   83.49%   -3.37%     
==========================================
  Files         120      120              
  Lines        7390     7423      +33     
==========================================
- Hits         6419     6198     -221     
- Misses        971     1225     +254     

Impacted Files	Coverage Δ
tensorly/regression/cp_regression.py	100.00% <100.00%> (ø)
tensorly/regression/tests/test_cp_regression.py	100.00% <100.00%> (ø)
tensorly/contrib/decomposition/_tt_cross.py	4.29% <0.00%> (-84.67%)	⬇️
...ecomposition/tests/test_mps_decomposition_cross.py	21.79% <0.00%> (-78.21%)	⬇️
tensorly/contrib/sparse/tests/test_tenalg.py	29.41% <0.00%> (-70.59%)	⬇️
...ensorly/contrib/sparse/tests/test_decomposition.py	41.17% <0.00%> (-58.83%)	⬇️
tensorly/utils/_prod.py	71.42% <0.00%> (-28.58%)	⬇️
tensorly/contrib/sparse/core.py	75.00% <0.00%> (-25.00%)	⬇️
tensorly/contrib/sparse/backend/__init__.py	75.86% <0.00%> (-10.35%)	⬇️
tensorly/backend/__init__.py	79.66% <0.00%> (-10.17%)	⬇️
... and 6 more

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[merajhashemi]

I will add new test cases for multi-dimensional outputs🙂

[aarmey]

This looks great @merajhashemi! Could you please run black formatting on the code? black tensorly in the top directory should do it.

[aarmey]

Check that I resolved the merge conflict correctly here.

[aarmey]

Indeed, I definitely think I messed up the merge here.