parquet: low memory arg

[ritchie46]

Added a low_memory argument to read/scan_parquet.

Currently this forces a slice to realloc. Really reducing memory pressure when we slice a small fraction of the complete array. This is at the expense of performance but when you are low on memory this might be worth it.

#3972

#3971

[codecov-commenter]

Codecov Report

Merging #4050 (fc86a3f) into master (396018b) will decrease coverage by 0.00%.
The diff coverage is 57.44%.

@@            Coverage Diff             @@
##           master    #4050      +/-   ##
==========================================
- Coverage   62.82%   62.82%   -0.01%     
==========================================
  Files         449      449              
  Lines       74440    74544     +104     
==========================================
+ Hits        46764    46829      +65     
- Misses      27676    27715      +39     

Impacted Files	Coverage Δ
.../polars-core/src/series/implementations/struct_.rs	56.55% <0.00%> (-1.19%)	⬇️
polars/polars-lazy/src/logical_plan/options.rs	56.75% <ø> (ø)
py-polars/polars/internals/frame.py	93.47% <ø> (+0.03%)	⬆️
py-polars/polars/internals/lazy_frame.py	76.00% <ø> (ø)
py-polars/polars/io.py	67.01% <ø> (ø)
polars/polars-core/src/frame/mod.rs	62.20% <14.28%> (-0.64%)	⬇️
polars/polars-io/src/parquet/read_impl.rs	89.65% <75.00%> (-0.31%)	⬇️
polars/polars-lazy/src/frame/parquet.rs	65.11% <80.00%> (+0.11%)	⬆️
polars/polars-io/src/parquet/read.rs	98.05% <100.00%> (+0.14%)	⬆️
polars/polars-lazy/src/logical_plan/builder.rs	90.29% <100.00%> (+0.04%)	⬆️
... and 30 more

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