Change the way of setting backends

[rogerwwww]

No description provided.

[codecov]

Codecov Report

Merging #87 (a4b2969) into main (dbfdad9) will decrease coverage by 0.04%.
Report is 2 commits behind head on main.
The diff coverage is 60.00%.

❗ Current head a4b2969 differs from pull request most recent head 1207071. Consider uploading reports for the commit 1207071 to get more accurate results

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
- Coverage   92.84%   92.80%   -0.04%     
==========================================
  Files          20       20              
  Lines        7600     7617      +17     
==========================================
+ Hits         7056     7069      +13     
- Misses        544      548       +4     

Files	Coverage Δ
pygmtools/__init__.py	80.85% <100.00%> (+5.85%)	⬆️
pygmtools/classic_solvers.py	87.50% <ø> (ø)
pygmtools/linear_solvers.py	84.21% <ø> (ø)
pygmtools/multi_graph_solvers.py	82.85% <ø> (ø)
pygmtools/neural_solvers.py	88.62% <ø> (ø)
pygmtools/utils.py	84.26% <28.57%> (-1.24%)	⬇️

... and 2 files with indirect coverage changes

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