chore: split off submodules from instruction.rs

[TomAFrench]

Description

Problem*

Resolves

Summary*

This PR decomposes instruction.rs into a couple of submodules based around different instruction types. This is done in the intention of breaking up the leviathan that is instruction.rs and making it easier to unit test in future.

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [Exceptional Case] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.