[Chronik] Add compress_script_variant to compress script variants

Summary:
Mirrors ScriptCompression in /src/compressor.h.

Having a Rust variant of this function allows us to avoid costly FFI bridging, which gets relevant in hot loops.

Test Plan: ninja check-crates

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D14426