Optimized slicing

[jorgecarleitao]

This PR drops the validity on slice and slice_unchecked when the resulting array has no null values. This:

• drops strong ref count, therefore allowing the validity to be freed earlier.
• allows users of the arrays to not have to check the validity's unset bits to branch an the faster case where there are no null values

Follow up of #1284

[codecov]

Codecov Report

Base: 83.02% // Head: 83.00% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (0bd58de) compared to base (cd985d4).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1285      +/-   ##
==========================================
- Coverage   83.02%   83.00%   -0.02%     
==========================================
  Files         364      364              
  Lines       39136    39145       +9     
==========================================
+ Hits        32491    32492       +1     
- Misses       6645     6653       +8     

Impacted Files	Coverage Δ
src/array/binary/mod.rs	91.55% <100.00%> (+1.00%)	⬆️
src/array/boolean/mod.rs	81.56% <100.00%> (+0.08%)	⬆️
src/array/fixed_size_binary/mod.rs	84.57% <100.00%> (+0.07%)	⬆️
src/array/fixed_size_list/mod.rs	82.20% <100.00%> (+0.10%)	⬆️
src/array/list/mod.rs	84.26% <100.00%> (+0.08%)	⬆️
src/array/map/mod.rs	59.37% <100.00%> (+0.25%)	⬆️
src/array/primitive/mod.rs	81.81% <100.00%> (+0.08%)	⬆️
src/array/struct_/mod.rs	61.66% <100.00%> (+0.21%)	⬆️
src/array/utf8/mod.rs	83.84% <100.00%> (+0.04%)	⬆️
src/array/equal/struct_.rs	46.34% <0.00%> (-24.40%)	⬇️
... and 3 more

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