refactor(node/service): remove SequencerActorBuilder

[einar-oplabs]

closes #3151

[codecov]

Codecov Report

❌ Patch coverage is 89.83051% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.8%. Comparing base (62657bf) to head (9507503).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/node/service/src/actors/sequencer/actor.rs	0.0%	3 Missing ⚠️
crates/node/service/src/service/node.rs	93.0%	3 Missing ⚠️

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[op-will]

Looks great.

Only small nitpicks, so please address as you see fit and merge after you verify tests pass 👍

[theochap]

Let's add an issue to add type-safety to ensure this actually never happens and we don't need to return an error

[op-will]

I think this needs to be moved into the if self.mode().is_sequencer() block or else it will break kona-node when run as a validator.

[op-will]

Let's add an issue...

I think the easiest approach here is to:

1. always create these channels
2. inject the other end into the EngineActor
3. Only use them if self.mode().is_sequencer()

Since spawn_and_wait! hangs, the sequencer side won't be dropped if running as a validator, but we should probably handle that case gracefully (continuing on rather than erring) in EngineActor

[einar-oplabs]

Assuming tests pass, can we merge this PR as is please?

Moving forward, I am happy to create channels unconditionally or alternative (and not necessarily better) we can create Option channels.

I created this issue #3179. Was that what you had in mind, when you mentioned type-safety, @theochap?

[theochap]

Love the negative diff, a few comments