refactor: Add FunctionCastOptions and conservative IR-level cast type-checking

[coastalwhite]

This changes three main things:

1. Refactor FunctionsOptions::cast_to_supertypes to FunctionOptions::cast_options in preparation for feat: Add index_of() function to Series and Expr #19894.
2. Immediately prune casts when they are added into the IR through function upcasting
3. Do some conservative cast type-checking in the IR. For instance, if you try to cast from a Boolean to a DateTime, it is now rejected in the type_coercion stage.

[codecov]

Codecov Report

Attention: Patch coverage is 80.47619% with 41 lines in your changes missing coverage. Please review.

Project coverage is 79.61%. Comparing base (f599e88) to head (51ad478).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-core/src/datatypes/dtype.rs	35.29%	22 Missing ⚠️
...ars-plan/src/plans/conversion/type_coercion/mod.rs	86.29%	17 Missing ⚠️
...an/src/plans/conversion/type_coercion/functions.rs	80.00%	1 Missing ⚠️
crates/polars-plan/src/plans/options.rs	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20286      +/-   ##
==========================================
+ Coverage   79.59%   79.61%   +0.01%     
==========================================
  Files        1565     1565              
  Lines      218462   218388      -74     
  Branches     2475     2477       +2     
==========================================
- Hits       173885   173860      -25     
+ Misses      44010    43962      -48     
+ Partials      567      566       -1     

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