[interpreter] Return INTEGER_OVERFLOW or BAD_INTEGER_ENCODING instead of UNKNOWN

Summary:
Currently, the Script interpreter returns UNKNOWN when it encountered an integer overflow or a non-minimally encoded integer.

This has been a nuisance for new Script devs for a while, because "unknown error" sounds like the interpreter is broken, but it's actually expected behavior.

Also, this makes script number tests more brittle.

Instead, we return INTEGER_OVERFLOW if there's been any kind of integer overflow, e.g. when parsing operands, or when executing an operation like OP_ADD, OP_BIN2NUM, etc.

Test Plan: ninja check && ninja check-functional

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D18481