Move maximum ExExManager capacity to a constant

[shekhirin]

Describe the feature

reth/crates/node/builder/src/launch/exex.rs

Lines 98 to 110 in 37b0c56

	// todo(onbjerg): rm magic number
	let exex_wal = Wal::new(
	config_container
	.config
	.datadir
	.clone()
	.resolve_datadir(config_container.config.chain.chain())
	.exex_wal(),
	)?;
	let exex_manager = ExExManager::new(
	exex_handles,
	1024,
	exex_wal,

This magic number 1024 on line 109 should be moved to a constant but not removed from the ExExManager::new arguments, so that we can still test the functionality of limiting the capacity.

1024 notifications in the buffer is 3.5 hours of mainnet blocks, or 17 minutes of 1-second blocks. It should be enough for any use-case, and we can make it configurable once there's a demand for that.

Additional context

No response

[nkysg]

may I take this?