Refactor out external parts to generics

Also creates a dedicated file for the message log.

substrate/tendermint/tests/ext.rs

@@ -0,0 +1,29 @@
+use tendermint_machine::ext::{BlockError, Block, Network};
+
+#[derive(Clone, PartialEq)]
+struct TestBlock {
+  id: u32,
+  valid: Result<(), BlockError>,
+}
+
+impl Block for TestBlock {
+  type Id = u32;
+
+  fn id(&self) -> u32 {
+    self.id
+  }
+}
+
+struct TestNetwork;
+impl Network<u16, TestBlock> for TestNetwork {
+  fn total_weight(&self) -> u64 {
+    5
+  }
+  fn weight(&self, id: u16) -> u64 {
+    [1, 1, 1, 1, 1][usize::try_from(id).unwrap()]
+  }
+
+  fn validate(&mut self, block: TestBlock) -> Result<(), BlockError> {
+    block.valid
+  }
+}