transforms: (dce) region-level dce

[alexarice]

Introduces a region level algorithm for dead-code elimination, which is capable of deleting unused operations which occur in cycles and deleting blocks. It is modeled on the mlir implementation. While the mlir implementation separates this into two separate passes (removing dead blocks and then removing dead operations) they have a todo comment for merging them, and so I have implemented it here as a single pass.

I have not implemented removal of block argument removal, for the sake of keeping this PR smaller and my own sanity, as it seems to add a fair bit of complexity.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.93%. Comparing base (f6c5960) to head (a6c96d7).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3253      +/-   ##
==========================================
+ Coverage   89.92%   89.93%   +0.01%     
==========================================
  Files         441      442       +1     
  Lines       55417    55499      +82     
  Branches     8643     8665      +22     
==========================================
+ Hits        49832    49913      +81     
- Misses       4158     4159       +1     
  Partials     1427     1427              

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