Bump MSRV to 1.57

[YuhanLiin]

No description provided.

[codecov-commenter]

Codecov Report

Merging #230 (8061956) into master (d4bd9c9) will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #230      +/-   ##
==========================================
- Coverage   55.44%   55.26%   -0.18%     
==========================================
  Files          95       95              
  Lines        8774     8750      -24     
==========================================
- Hits         4865     4836      -29     
- Misses       3909     3914       +5     

Impacted Files	Coverage Δ
src/dataset/impl_targets.rs	21.31% <ø> (ø)
...gorithms/linfa-preprocessing/src/linear_scaling.rs	72.03% <0.00%> (-4.24%)	⬇️
algorithms/linfa-bayes/src/base_nb.rs	62.96% <0.00%> (-3.71%)	⬇️
algorithms/linfa-kernel/src/lib.rs	60.21% <0.00%> (-3.06%)	⬇️
src/composing/multi_target_model.rs	64.44% <0.00%> (-3.00%)	⬇️
algorithms/linfa-svm/src/permutable_kernel.rs	45.12% <0.00%> (-1.87%)	⬇️
...linfa-clustering/src/appx_dbscan/cells_grid/mod.rs	49.12% <0.00%> (-1.76%)	⬇️
algorithms/linfa-nn/src/balltree.rs	54.33% <0.00%> (-1.58%)	⬇️
...lgorithms/linfa-clustering/src/optics/algorithm.rs	48.82% <0.00%> (-1.47%)	⬇️
algorithms/linfa-hierarchical/src/lib.rs	41.66% <0.00%> (-0.59%)	⬇️
... and 23 more

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