Reduce monomorphized code in execute_maybe_iterate

[MichaReiser]

The execute_maybe_iterate function is rather large but not all of its code is generic over C.

This PR extracts the not-generic code into a few helper functions to reduce the size of the compiled code.

Before, many functions with cycle handling generated about 8KB of code each (often beeing within the largest functions of the entire ty binary).
This PR reduces the size to about 5KB each (results in a 200KB reduction overall)

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #1046 will not alter performance

_{Comparing MichaReiser:avoid-monomorphization-execute-maybe-iterate (1ca0621) with master (ce80691)}

Summary

✅ 13 untouched