fix: Bitwise aggregations should ignore null values

[orlp]

Fixes #19065.

Also fixes #19066.

[codecov]

Codecov Report

Attention: Patch coverage is 32.43243% with 50 lines in your changes missing coverage. Please review.

Project coverage is 79.77%. Comparing base (b1b322f) to head (d9f9d17).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-python/src/series/aggregation.rs	0.00%	27 Missing ⚠️
crates/polars-compute/src/bitwise/mod.rs	51.61%	15 Missing ⚠️
...olars-core/src/chunked_array/ops/bitwise_reduce.rs	50.00%	5 Missing ⚠️
py-polars/polars/series/series.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19067      +/-   ##
==========================================
+ Coverage   79.75%   79.77%   +0.02%     
==========================================
  Files        1531     1531              
  Lines      208547   208500      -47     
  Branches     2913     2913              
==========================================
+ Hits       166319   166333      +14     
+ Misses      41677    41616      -61     
  Partials      551      551              

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