unify timestamp handling throughout the stack

[benluelo]

currently, we define timestamps as multiple different types:

union/lib/unionlabs/src/traits.rs

Lines 152 to 153 in f92cc97

	/// Query the latest finalized timestamp of this chain.
	fn query_latest_timestamp(&self) -> impl Future<Output = Result<i64, Self::Error>> + '_;

union/lib/unionlabs/src/traits.rs

Lines 310 to 312 in f92cc97

	pub trait ConsensusState {
	fn timestamp(&self) -> u64;
	}

this should be unified to a type that handles nanos properly. we can likely reuse the protobuf defined timestamp type: https://github.com/unionlabs/union/blob/main/lib/unionlabs/src/google/protobuf/timestamp.rs

[benluelo]

not marking this as E-easy since this touches a significant portion of the repo