Keep track of epoch in the test Datastore

[hugocaillard]

Since recent Clarity 3 changes, the data store (used in the tests in this project) needs to be able to return epoch information.

clarity-wasm/clar2wasm/src/datastore.rs

Lines 567 to 575 in 93eace4

	fn get_stacks_epoch(&self, _height: u32) -> Option<StacksEpoch> {
	Some(StacksEpoch {
	epoch_id: StacksEpochId::latest(),
	start_height: 0,
	end_height: u64::MAX,
	block_limit: ExecutionCost::max_value(),
	network_epoch: PEER_VERSION_EPOCH_2_1,
	})
	}

Right now, the Epoch ID is hard coded. For better tests, we may want to keep track of the epoch in the data store.
If that's useful, check clarinet implementation of this