feat: publish synced flashblocks to ws

[noot]

📝 Summary

• publish synced flashblocks via websocket as well

✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)

[Copilot]

Pull Request Overview

This PR extends the flashblocks feature to publish synced flashblocks via WebSocket in addition to the existing P2P publishing mechanism. The main architectural change moves WebSocket publisher initialization to the service level so it can be shared between the payload builder (for locally built blocks) and payload handler (for synced blocks).

Key Changes:

• WebSocket publisher is now instantiated at the service level and passed to both payload builder and handler components
• Payload handler enhanced to publish received/synced flashblocks via WebSocket after successful execution
• Refactored OpPayloadBuilder::new() to accept pre-initialized WebSocket publisher instead of creating it internally

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
service.rs	Instantiates WebSocket publisher at service level and passes it to payload builder and handler
payload_handler.rs	Adds WebSocket publishing for synced flashblocks with metrics recording
payload.rs	Refactors constructor to accept WebSocket publisher as parameter instead of creating it
ctx.rs	Adds accessor method for metrics used in publishing

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[SozinM]

What's the point of this?
I see that it's a little bit useful once we have consensus between builders, but right now seems like it's not usable (we would just post flashblocks from different builders?)

[noot]

@SozinM it would allow RPC providers to get the flashblock stream from non-active builders as well, and allows us to easily ensure that the non-active builders are syncing properly.