Replace warnings about potential endless loops by timeouts and error messages

[maehw]

The generator may spit out several warning messages like the following:

[ WARNING] Entering potential endless loop (trying to merge AND gates)

This has been added as the generator is known to hang for some designs. The root cause is currently unknown - as it simply has not been analyzed yet.

Design to reproduce: https://github.com/maehw/wokwi-lookup-table-generator/blob/main/demos/4bit-popcount.logic.json

This may be helpful, but is also annoying as the warning messages will appear for every design.

A better way to detect endless loops would be to use timeouts (wait for some time and abort when the loop has not finished yet). Those timeouts may be dynamic as they should grow with the design complexity (or input/output size). But we could also use a static timeout as the machines to run the generator on should not be too low.