Allow divide_dim to divide to non-literal expressions

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.30435% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 87.01%. Comparing base (0e2ec87) to head (df33a58).

Files	Patch %	Lines
src/exo/LoopIR_scheduling.py	87.50%	4 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #628 +/- ## ======================================= Coverage 87.00% 87.01% ======================================= Files 94 94 Lines 21814 21838 +24 ======================================= + Hits 18979 19002 +23 - Misses 2835 2836 +1 ```

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