SSA: Handle non-admissible stack shuffler results

[LeviofCrypto]

This changes the SSA stack shuffler call sites to stop asserting that every shuffle is admissible. Instead, the code routes non-admissible results through requireAdmissibleShuffle(), which turns StackTooDeep into StackTooDeepError and unexpected statuses into InternalCompilerError with context about the source and target stacks.

The helper is used in SSA code generation, stack layout generation, and target-size evaluation so failures are surfaced consistently from the actual consumer sites. The change also adds unit coverage for the new error mapping and wires the test into soltest.

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[clonker]

Hi, thank you very much for your efforts, it is appreciated! However currently the SSA-CFG backend is in flux and especially the parts you are touching here are precisely the ones that are bound to change once stack-to-deep handling is implemented. The very changes you are making here would have to be undone at least to some degree. Therefore, I am closing this.