REF: Simplify _comp_method_SERIES
- Do raising checks earlier on, matching how this is done elsewhere (moving towards #23853) 
- Comment on line 1034 notes possibly-inconsistent behavior that we should either change or add an explanatory comment for.
- Ditto line 1058
- Before long we'll be able to collapse all of the dispatch_to_extension_op cases into one case; I'm still troubleshooting some corner cases of this on another branch.
- After this, `na_op` is only called in one place, meaning it will be easier to make further de-nesting/de-closuring simplifications in follow-ups.
- Putting all the finalize/_constructor business at the end will make it easier to separate out the array-specific middle and apply it to a) PandasArray and b) Block-wise.
thanks @jbrockmendel 