ExEx notification type targets finalized/safe blocktag

[mattsse]

Add Stream type that only yields a canonstate notififaction on new finalized/safe block.

This should be a helper wrapper type over

https://github.com/paradigmxyz/reth/blob/ead753db4c96f5f9f0fd2867106d88ef6d312405/crates/storage/provider/src/traits/chain.rs#L30-L30

that monitors buffers a Chain until a new finalized/safe block is reached, this info can be obtained from a Provider