[Chronik] Add Script and ScriptMut

Summary:
We use two structs to represent Bitcoin scripts:

• Script: An immutable and cheap to copy script.
• ScriptMut: A mutable script with helpful functions to modify scripts.

Depends on D13528.

Test Plan: ninja check-crates

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D13529