feat[rust, python]: add float_precision parameter to DataFrame.write_csv

[matteosantama]

Closes #4279 and #1125

Unfortunately lexical does not provide a way to specify the number of decimals to write (see this comment) but we still use the fast-path when no float_precision is specified (by default).

[ritchie46]

Thanks. I have a few minor remarks.

[matteosantama]

Removed all benchmarking code

[codecov-commenter]

Codecov Report

Merging #4504 (35e70b4) into master (de93b31) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4504      +/-   ##
==========================================
+ Coverage   79.33%   79.34%   +0.01%     
==========================================
  Files         493      493              
  Lines       77667    77708      +41     
==========================================
+ Hits        61614    61656      +42     
+ Misses      16053    16052       -1     

Impacted Files	Coverage Δ
py-polars/polars/internals/dataframe/frame.py	94.20% <ø> (ø)
polars/polars-io/src/csv/write.rs	98.41% <100.00%> (+0.16%)	⬆️
polars/polars-io/src/csv/write_impl.rs	86.44% <100.00%> (+5.67%)	⬆️
py-polars/src/dataframe.rs	91.15% <100.00%> (+0.01%)	⬆️
...ars/polars-core/src/series/implementations/utf8.rs	71.53% <0.00%> (-1.13%)	⬇️
polars/polars-core/src/series/series_trait.rs	13.33% <0.00%> (-1.06%)	⬇️
polars/polars-time/src/series/mod.rs	57.33% <0.00%> (-0.67%)	⬇️
polars/polars-lazy/src/logical_plan/iterator.rs	97.45% <0.00%> (-0.64%)	⬇️
polars/polars-core/src/utils/mod.rs	87.50% <0.00%> (-0.30%)	⬇️
...olars/polars-core/src/frame/groupby/into_groups.rs	58.67% <0.00%> (-0.28%)	⬇️
... and 8 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.