Improve engine event variants

[mattsse]

with #9670 we have the lower level event handling in place

we can consolidate some event variants for the engineapievent type

reth/crates/engine/tree/src/engine.rs

Lines 184 to 192 in ab861bd

	/// Events emitted by the engine API handler.
	#[derive(Debug)]
	pub enum EngineApiEvent {
	/// Event from the consensus engine.
	// TODO(mattsse): find a more appropriate name for this variant, consider phasing it out.
	BeaconConsensus(BeaconConsensusEngineEvent),
	/// Bubbled from tree.
	FromTree(TreeEvent),
	}

and get rid of the additional TreeEvent type