feat(sequencer): rework fee handling

[ethanoroshiba]

Summary

Added new fees component to hold all fee handling, which implements check_and_pay_fees() for each action.

Background

This is meant to streamline and standardize fee handling in a way that keeps the same functionality, but makes it more difficult to introduce bugs in fee handling in the future. Offline discussion suggested changing the return type of execute_transaction() to be our own type as opposed to Vec<Event>, but I think this would be best done in a followup, since deposit ABCI events are also recorded via apply().

Changes

• Added new component fees with trait FeeHandler and struct Fee.
• Created new function check_execute_and_pay_fees(), which first calls check_and_execute() and then calls FeeHandler::check_and_pay_fees(). Changed all actions to use this new function in place of check_and_execute()
• Moved all actions' fee handling from check_and_execute() to check_and_pay_fees().
• Changed block fee read/writes on the state delta to use the ephemeral cache with Vec<Fee>. This allows for end_block() to still pay out all fees at the end of the block, and create fee ABCI events at that time. Moved these to fees::state_ext.rs.

Testing

All previous tests passing.

Breaking Changelist

• Changed block fees storage key, as it does not need to incorporate the asset name into the storage key anymore. This breaks the app:state_ext::storage_keys_are_unchanged snapshot

Related Issues

closes #1369
closes #1145

[ethanoroshiba]

Should bridge sudo change action be deducting the fee from the signer as opposed to the bridge address?

[SuperFluffy]

I have two notes:

1. I don't see an advantage in changing AppHandler itself. The same thing can be done by creating a function and it keeps the AppHandler clean.

fn check_execute_and_pay_fees<T: AppHandler + FeeHandler, S: StateWrite>(action: &T, mut state: S) -> Result<()> {
    action.check_and_execute(state)?;
    action.pay_fees(state)?;
}

2. I think it would be nice to make a fees component and move all state accesses there.

[SuperFluffy]

I'd like to make the fields of this type private. All the impl FeeHandler for {Action} can/should subsequently be moved here.

[ethanoroshiba]

Made all fields private but added accessors for asset and amount so that fees can be paid out during end_block

[SuperFluffy]

Now that we start making use of this API, it has some obvious warts: we should be able to obtain a mutable reference to the object (if it exists), so that we don't need to clone it out and back into the ephemeral store.

CC @Fraser999 for the rework of the state delta construction.