docs: polars-lazy readability improvements

[ryanrussell]

Separated out the two code re-wordingsto make them easier to read:

• replace_wildcard
• excluded

Rest of the changes are mostly comments.

Best,
Ryan

[codecov-commenter]

Codecov Report

Merging #3701 (604da7b) into master (0307a57) will increase coverage by 5.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3701      +/-   ##
==========================================
+ Coverage   72.35%   77.69%   +5.33%     
==========================================
  Files         436      436              
  Lines       72836    72836              
==========================================
+ Hits        52704    56592    +3888     
+ Misses      20132    16244    -3888     

Impacted Files	Coverage Δ
...y/src/logical_plan/optimizer/aggregate_pushdown.rs	0.00% <ø> (ø)
...s/polars-lazy/src/physical_plan/expressions/mod.rs	83.16% <ø> (+7.90%)	⬆️
polars/polars-lazy/src/utils.rs	82.05% <ø> (+32.23%)	⬆️
py-polars/src/dataframe.rs	89.00% <ø> (ø)
polars/polars-lazy/src/logical_plan/projection.rs	90.79% <100.00%> (ø)
...ars/polars-lazy/src/physical_plan/executors/mod.rs	97.18% <100.00%> (+6.33%)	⬆️
py-polars/src/series.rs	78.20% <100.00%> (ø)
...core/src/chunked_array/logical/categorical/from.rs	21.62% <0.00%> (-18.92%)	⬇️
...s/polars-core/src/chunked_array/upstream_traits.rs	73.04% <0.00%> (-2.61%)	⬇️
polars/polars-io/src/parquet/predicates.rs	68.88% <0.00%> (-2.23%)	⬇️
... and 136 more

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[ritchie46]

Thanks!