[#37] generalize failing instructions in Indigo

Description

Failing instructions in Indigo are currently implemented with a fixed output value of () and also having the output stack be the same as the input one.

With this MR failWith is now part the erroring instructions in Indigo and the existing ones have been modified to have arbitrary output value and stack.

To be able to do this, they use a generic error for both, which in turn required the output value to be lazy. For this reason GenCode has been modified to also contain it and replace the tuple that previously was the result of an IndigoM computation.

Related issue(s)

Resolves #37 (closed)

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