Fixed bug in writing csv with buffer resizing

[ritchie46]

This fix a bug where we didn't correctly resize the buffer when encoding csv fields. We also remove the loop as it is not needed, we can simply ensure to alloc enough without looping.

Fixes pola-rs/polars#3232

[codecov]

Codecov Report

Merging #965 (3e92f8c) into main (e478619) will increase coverage by 0.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #965      +/-   ##
==========================================
+ Coverage   71.42%   71.43%   +0.01%     
==========================================
  Files         355      355              
  Lines       19572    19572              
==========================================
+ Hits        13980    13982       +2     
+ Misses       5592     5590       -2     

Impacted Files	Coverage Δ
src/io/csv/write/serialize.rs	62.65% <66.66%> (+1.60%)	⬆️
src/bitmap/utils/slice_iterator.rs	86.20% <0.00%> (-1.73%)	⬇️
src/compute/arithmetics/time.rs	25.68% <0.00%> (-0.92%)	⬇️

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