Fix is_syncing API reporting when head is synced optimistically

[StefanBratanov]

PR Description

When we optimistically track head and sync distance is 0, technically we should report is_syncing: false even though we are waiting for the EL.

Fixed Issue(s)

fixes #8888

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[mehdi-aouadi]

I'm a bit bothered by the logic difference between the API and the SyncStateTracker: the latter doesn't take the slots behind into consideration at all to mark the node IN_SYNC. This definitely fixes the issue we have though.
I'm wondering if it wouldn't be better to first check the SyncStateTracker to see if the node is IN_SYNC otherwise consider checking the slot behind...
Not a strong opinion here, just making sure we cover all the cases...

[StefanBratanov]

I'm a bit bothered by the logic difference between the API and the SyncStateTracker: the latter doesn't take the slots behind into consideration at all to mark the node IN_SYNC. This definitely fixes the issue we have though. I'm wondering if it wouldn't be better to first check the SyncStateTracker to see if the node is IN_SYNC otherwise consider checking the slot behind... Not a strong opinion here, just making sure we cover all the cases...

I had a look at the SyncStateTracker and we have this notion that if we are AWAITING_EL (tracking optimistic head with sync_distance = 0) then we are still syncing and isInSync() returns false. This cascades to a few places in the code, specifically around the fact that when we are tracking optimistic head, we shouldn't perform any duties and also in onTick(). I think I would raise an issue instead explaining this and leave this change relatively simple only impacting the API code.

[StefanBratanov]

Raised #8890 to track usages of isInSync

[mehdi-aouadi]

Let's fix the API and we'll review the SyncStateTracker in the issue you raised. Thanks!