transformations: Make loop folding consistent with mlir

[mamanain]

There was a difference in logic between this pass in mlir and xdsl and xdsl's version made it hard to flatten ptr loops. Made the logic consistent.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.23%. Comparing base (805ea3e) to head (a1b9d5c).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4037      +/-   ##
==========================================
+ Coverage   90.19%   90.23%   +0.04%     
==========================================
  Files         458      458              
  Lines       58337    58365      +28     
  Branches     5692     5687       -5     
==========================================
+ Hits        52616    52667      +51     
+ Misses       4331     4317      -14     
+ Partials     1390     1381       -9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[superlopuh]

Let's not merge this end-to-end test

[superlopuh]

Nice!