Improved performance of writing to CSV (20-25%)

[jorgecarleitao]

Currently, we write to CSV by using an Iterator<Item=Vec<u8>>. This requires a new allocation per non-null item.

This PR uses StreamingIterator to significantly reduce the number of allocations.

A StreamingIterator is an Iterator-like trait that allows yielding references of itself, &[u8] in this case. We maintain an internal buffer of Vec<u8> on the (streaming) iterator and re-use it across items within the array.

In summary, this replaces (1 alloc + write bytes) by a (maybe 1 realloc + write bytes) per non-null item. For types that require a fixed number of bytes (e.g. all our primitive types), it results in a single allocation per array, as opposed to an allocation per non-null item.

csv write i32 2^18      time:   [15.828 ms 15.866 ms 15.915 ms]                               
                        change: [-26.127% -25.784% -25.480%] (p = 0.00 < 0.05)
csv write utf8 2^18     time:   [33.100 ms 33.188 ms 33.276 ms]                                
                        change: [-14.104% -13.811% -13.508%] (p = 0.00 < 0.05)
csv write f64 2^18      time:   [23.661 ms 23.702 ms 23.748 ms]                               
                        change: [-20.623% -20.448% -20.239%] (p = 0.00 < 0.05)

[codecov]

Codecov Report

Merging #382 (964ca91) into main (b16d6b9) will increase coverage by 0.02%.
The diff coverage is 61.90%.

@@            Coverage Diff             @@
##             main     #382      +/-   ##
==========================================
+ Coverage   81.11%   81.14%   +0.02%     
==========================================
  Files         330      331       +1     
  Lines       21770    21891     +121     
==========================================
+ Hits        17659    17763     +104     
- Misses       4111     4128      +17     

Impacted Files	Coverage Δ
src/io/csv/write/mod.rs	76.00% <50.00%> (ø)
src/io/csv/write/serialize.rs	46.15% <57.14%> (+5.85%)	⬆️
src/io/csv/write/iterator.rs	71.42% <71.42%> (ø)
src/util/lexical.rs	75.00% <80.00%> (+12.50%)	⬆️
src/array/boolean/ffi.rs	0.00% <0.00%> (-5.89%)	⬇️
tests/it/array/primitive/mod.rs	100.00% <0.00%> (ø)
src/array/display.rs	61.70% <0.00%> (+2.57%)	⬆️
src/temporal_conversions.rs	85.00% <0.00%> (+5.00%)	⬆️

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