chore(sequencer): consolidate all action handling to one module

[ethanoroshiba]

Summary

Moved all action and transaction handling to single module.

Background

Previously, all implementations of ActionHandler were done separately in components which corresponded to their given actions (or groups of actions, such as in bridge). While this may make sense from an action-centered point of view, it is confusing to an outsider to have to look many different places to find where stateless/stateful checks and execution occur. This PR consolidates all of the implementations as well as their testing.

Changes

• Created new action_handler module and moved the corresponding ActionHandler trait as well as all of its impls into this module.
• Renamed some moved tests for clarity.
• Categorized tests by action in submodule tests.
• Categorized impls by action in submodule impls.

Testing

Passing all tests.

Changelogs

Changelogs updated

Related Issues

closes #1657

[Fraser999]

Could the unit tests for each action be moved from the common action_handler::tests module back into the modules specific to each individual unit under test please?

Generally I think it's good practice to keep unit tests as close to the unit under test as possible, but it will probably also help with this review since we'll see mostly files being moved with minimal changes, whereas just now we see a lot of files being added and deleted.

I'm also not sure that we need the impls submodule - I'd be inclined to just flatten this into action_handler, but I don't feel very strongly about that.