Modify Relayer service to order Events from L1 by block index

[MitchTurner]

closes #1772

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Had to modify MockDB to also maintain order.

This code only works if the Relayer DB maintains order. In production it is stored as a Mappable with value being [Event]:

impl Mappable for EventsHistory {
    /// The key is the height of the DA.
    type Key = Self::OwnedKey;
    type OwnedKey = DaBlockHeight;
    /// The value is an events happened at the height.
    type Value = [Event];
    type OwnedValue = Vec<Event>;
}

So it should be good.

This approach is flakier than having the relayer reader in the executor ensure the order, but it could add a lot of extra execution cost to the executor code if we put the sorting on that side. We are already making assumptions about what the writing code is doing though. For example, if an event is missing from L1, correct order doesn't matter. So why not add more assumptions :P

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We require that all Logsinclude the log_index so we can sort them. So I added a test relayer__if_a_log_does_not_include_index_then_event_not_included to check the sad path. I'm not positive this is the behavior we want. It is erroring in the sort_events_by_log_index method but I'm not exactly sure where that bubbles up to: start_and_await still returns an Ok(Starting) not an Ok(StoppedWithError). That might be a bug in our Service code, or might be meant to be used differently. Not sure. So I just check that the Log isn't included in the test...

I had to modify MockMiddleware to only let you take the batch once. Before it would error and then just try again and call the same value over and over and never exited. Making some assumptions there too.

[MitchTurner]

The alternative here would be set to 0 if None.

I think I prefer the error, but there are still ways for this to be non-deterministic, e.g. if there are more than one log with the same index.

So, maybe we need to have additional checks that there are no duplicates? And do we want to accept batches with missing log indices?

If we don't want to worry about all the edge cases, then we could just do .unwrap_or(0) instead of .ok_or?

[MitchTurner]

Talked to the team about this offline. It sounds like we are okay with throwing an error here and not including the batch. In practice, this value should always be Some.

In a similar vein, we can probably assume they will always be in order and all unique.

[Voxelot]

Are all events coming through this sort helper fn guaranteed to be grouped by da_height?

[MitchTurner]

They get sorted into blocks after they are sorted by index. So it will maintain order once sorted by block.

[MitchTurner]

The can_paginate_logs and test_da_height_updates shouldn't exist. I kept them because my changes broke them, but just because our MockMiddleware changed behavior, not because of changed business code.

Instead of can_paginate_logs there should be a MockMiddleware that returns values in batches and we should show that they are stitched together correctly. download_logs shouldn't be the SUT--it's not even public.

[xgreenx]

We need to return an error if retry_on_error == true