Add flake8-tidy-imports extension

[stinodego]

Relates to #4044

Changes:

• Add the flake8-tidy-imports extension
• Add setting to ban relative imports
• Fix linting errors

[codecov-commenter]

Codecov Report

Merging #4229 (5caae84) into master (2dbc6bf) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4229      +/-   ##
==========================================
+ Coverage   64.09%   64.16%   +0.07%     
==========================================
  Files         458      458              
  Lines       75675    75729      +54     
==========================================
+ Hits        48502    48592      +90     
+ Misses      27173    27137      -36     

Impacted Files	Coverage Δ
py-polars/polars/__init__.py	100.00% <100.00%> (ø)
py-polars/polars/internals/__init__.py	100.00% <100.00%> (ø)
py-polars/polars/internals/frame.py	91.55% <100.00%> (ø)
...ars/polars-core/src/chunked_array/ops/any_value.rs	77.39% <0.00%> (-0.87%)	⬇️
polars/polars-core/src/series/from.rs	65.00% <0.00%> (-0.59%)	⬇️
...lars/polars-core/src/chunked_array/builder/list.rs	62.29% <0.00%> (-0.28%)	⬇️
polars/polars-io/src/csv/buffer.rs	79.39% <0.00%> (-0.26%)	⬇️
.../polars-core/src/frame/groupby/aggregations/mod.rs	63.08% <0.00%> (ø)
...ars-core/src/chunked_array/ops/take/take_single.rs	44.23% <0.00%> (ø)
...lars/polars-lazy/src/physical_plan/planner/expr.rs	92.94% <0.00%> (+0.08%)	⬆️
... and 11 more

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[ritchie46]

Thanks @stinodego. There is a conflicting file and then I can merge.

[stinodego]

Rebased & ready to go 😎