chore: split off submodules from instruction.rs (#4084)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## 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:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.