Simplify Rewrite Rules in squin -> stim pass

[johnzl-777]

There's a comment I left in my squin to stim rewrite pass but basically, with observations from the team in reviews on #19 there's a lot of duplicate logic that can be consolidated and simplified into smaller rewrite rules (as opposed to what I had in the beginning, which was this gigantic monolithic rewrite pass that attempted to do EVERYTHING for squin).

This is very low priority but would make testing and maintaining things significantly easier.

[johnzl-777]

Revisiting the current state of squin to stim I believe things have been sufficiently simplified/made modular (although since that time the size of the pass has naturally grown to handle previously unaccounted for cases)