12a1c3c4b7 Add `script` tests (Jamil Lambert, PhD)
Pull request description:
Together with #3971 this fixes all of the mutants in `primitives/src/script` except for those related to `serde`.
ACKs for top commit:
tcharding:
ACK 12a1c3c4b7
apoelstra:
ACK 12a1c3c4b7bc097553fbfb05a0e92320ae42975c; successfully ran local tests
Kixunil:
ACK 12a1c3c4b7
Tree-SHA512: c0b757ae672999799e105befb6a2907b8cecb54c3e6d86dbf3e877ddf54e6fd102ebb2604381d0fa89bce0b3b4f70db6cb9ed3b5c85076e13de8369e81431926