refactor: Fix struct outer validity;fmt;is_in;cast;cmp

[ritchie46]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 94.28571% with 4 lines in your changes missing coverage. Please review.

Project coverage is 80.47%. Comparing base (a098ed1) to head (81a7096).
Report is 1 commits behind head on main.

Files	Patch %	Lines
...ates/polars-core/src/chunked_array/ops/downcast.rs	90.32%	3 Missing ⚠️
...rates/polars-core/src/chunked_array/struct_/mod.rs	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17590      +/-   ##
==========================================
+ Coverage   80.44%   80.47%   +0.03%     
==========================================
  Files        1484     1484              
  Lines      195532   195647     +115     
  Branches     2778     2780       +2     
==========================================
+ Hits       157299   157452     +153     
+ Misses      37721    37683      -38     
  Partials      512      512              

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