Allow visit_custom recursion to change the order

[Keno]

To implement order-changing intrinsics.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 ⚠️

Comparison is base (efbb0f4) 52.44% compared to head (437aa38) 52.42%.

❗ Current head 437aa38 differs from pull request most recent head 63354cc. Consider uploading reports for the commit 63354cc to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
- Coverage   52.44%   52.42%   -0.03%     
==========================================
  Files          27       27              
  Lines        2723     2726       +3     
==========================================
+ Hits         1428     1429       +1     
- Misses       1295     1297       +2     

Impacted Files	Coverage Δ
src/stage1/recurse_fwd.jl	57.57% <ø> (ø)
src/tangent.jl	39.23% <ø> (ø)
src/codegen/forward_demand.jl	45.57% <100.00%> (+0.82%)	⬆️

... and 1 file with indirect coverage changes

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[oscardssmith]

should we merge this?

[staticfloat]

@Keno can you add a simple test that changes the order?

[oxinabox]

This makes sense.
One comment that is unrelated to the bulk of this