[Chronik] Add ScriptGroup to group txs by script

Summary:
An implementation of Group for grouping by script.

We cannot use ffi::compress_script directly here, as the tests can't link against that, so instead it is a field in ScriptGroup.

We also remove the chronik-bridge dependency as we don't need it.

Test Plan: ninja check-crates

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13544