[When] Split when blocks with cycles

[leonardt]

Fixes #1269

Adds a pass that splits when blocks with a cyclic dependency.

Note the generated verilog can have empty blocks since some of the assignments are being emitted in a split block, but this seems to be okay for verilator. Since this is likely to be an uncommon case, I don't think we should worry too much about trying to cleanup the generated verilog.

[codecov-commenter]

Codecov Report

Patch coverage: 97.19% and project coverage change: +0.17% 🎉

Comparison is base (382edd3) 85.90% compared to head (00f0a7f) 86.08%.
Report is 81 commits behind head on fix-1253.

❗ Current head 00f0a7f differs from pull request most recent head c1b119d. Consider uploading reports for the commit c1b119d to get more accurate results

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Additional details and impacted files

@@             Coverage Diff              @@
##           fix-1253    #1309      +/-   ##
============================================
+ Coverage     85.90%   86.08%   +0.17%     
============================================
  Files           164      170       +6     
  Lines         17637    17818     +181     
============================================
+ Hits          15151    15338     +187     
+ Misses         2486     2480       -6     

Files Changed	Coverage Δ
magma/backend/mlir/build_magma_graph.py	93.00% <ø> (+0.19%)	⬆️
magma/backend/mlir/common.py	95.83% <ø> (+2.08%)	⬆️
magma/backend/mlir/hw.py	98.56% <50.00%> (ø)
magma/backend/mlir/translation_unit.py	91.60% <50.00%> (-0.65%)	⬇️
magma/array.py	89.29% <75.00%> (-0.22%)	⬇️
magma/tuple.py	89.87% <87.50%> (+0.39%)	⬆️
magma/primitives/when.py	96.04% <90.32%> (-1.95%)	⬇️
magma/mantle/counter.py	96.66% <96.66%> (ø)
magma/__init__.py	93.05% <100.00%> (+0.09%)	⬆️
magma/backend/mlir/compile_to_mlir_opts.py	100.00% <100.00%> (ø)
... and 16 more

... and 1 file with indirect coverage changes

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[rsetaluri]

Final minor comment