Expanse Byzantium update w/ correct metropolis difficulty increment divisor (#7463)

* Byzantium Update for Expanse

Here the changes go. Hope I didnt miss anything.

* expip2 changes - update duration limit

* Fix missing EXPIP-2 fields

* Format numbers as hex

* Fix compilation errors

* Group expanse chain spec fields together

* Set metropolisDifficultyIncrementDivisor for Expanse

* Revert #7437

* Add Expanse block 900_000 hash checkpoint

json/src/spec/ethash.rs

@@ -125,6 +125,14 @@ pub struct EthashParams {
 	/// EIP-649 base reward.
 	#[serde(rename="eip649Reward")]
 	pub eip649_reward: Option<Uint>,
+
+	/// EXPIP-2 block height
+	#[serde(rename="expip2Transition")]
+	pub expip2_transition: Option<Uint>,
+
+	/// EXPIP-2 duration limit
+	#[serde(rename="expip2DurationLimit")]
+	pub expip2_duration_limit: Option<Uint>,
 }
 
 /// Ethash engine deserialization.
@@ -241,6 +249,8 @@ mod tests {
 				eip649_transition: None,
 				eip649_delay: None,
 				eip649_reward: None,
+				expip2_transition: None,
+				expip2_duration_limit: None,
 			}
 		});
 	}
@@ -287,6 +297,8 @@ mod tests {
 				eip649_transition: None,
 				eip649_delay: None,
 				eip649_reward: None,
+				expip2_transition: None,
+				expip2_duration_limit: None,
 			}
 		});
 	}