[Feature] Add engine api extension

[mattsse]

Component

provider, pubsub, rpc

Describe the feature you would like

mostly for testing purposes, it would be nice to have an EngineApiExt trait similar to

alloy/crates/provider/src/ext/admin.rs

Line 11 in c058e32

pub trait AdminApi<N, T>: Send + Sync {

see also:

https://github.com/paradigmxyz/reth/blob/0938504f4a265eec74e0b833ab5c41d66649bdee/crates/rpc/rpc-api/src/engine.rs#L27-L27

TODO

• add extension trait for engine API
• can use ethereum engine types, but I think eventually we'd need a helper trait because some request params are also network specific
• should be feature gated because not useful for regular usage

Additional context

No response

[leruaa]

I can take this on.

[leruaa]

@mattsse May I continue on that topic by replacing the trait in Reth https://github.com/paradigmxyz/reth/blob/0938504f4a265eec74e0b833ab5c41d66649bdee/crates/rpc/rpc-api/src/engine.rs#L27-L27 by the new trait from Alloy?

Assuming Alloy rev in Reth will need to be bumped obviously ;)

[mattsse]

we still need this because this also generates the server code