Add coordinator rotation test (#535)

* add node side unit test

* complete rotation test for all networks

* set up the fast-epoch docker file

* fix pr comments

* add coordinator side rotation test

* bug fixes

* Remove EPOCH_INTERVAL

* Minor nits

* Add note on origin of publish_tx function in tests/coordinator

* Correct ThresholdParams assert_eq

* fmt

* Correct detection of handover completion

* Restore key gen message match from develop

It was modified in response to the handover completion bug, which has now been
resolved.

* bug fixes

* Correct invalid constant

* Typo fixes

* remove selecting participant to remove at random

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

substrate/client/src/serai/mod.rs

@@ -195,10 +195,10 @@ impl Serai {
   }
 
   async fn active_network_validators(&self, network: NetworkId) -> Result<Vec<Public>, SeraiError> {
-    let hash: String = self
+    let validators: String = self
       .call("state_call", ["SeraiRuntimeApi_validators".to_string(), hex::encode(network.encode())])
       .await?;
-    let bytes = Self::hex_decode(hash)?;
+    let bytes = Self::hex_decode(validators)?;
     let r = Vec::<Public>::decode(&mut bytes.as_slice())
       .map_err(|e| SeraiError::ErrorInResponse(e.to_string()))?;
     Ok(r)