Add default implementations to Component trait

This allows components that don't do anything for a particular method to skip implementing it at
all.

crates/core/component/component/src/component.rs

@@ -18,7 +18,7 @@ pub trait Component {
     /// This method is called once per chain, and should only perform
     /// writes, since the backing tree for the [`State`] will
     /// be empty.
-    async fn init_chain<S: StateWrite>(state: S, app_state: &Self::AppState);
+    async fn init_chain<S: StateWrite>(_state: S, _app_state: &Self::AppState) {}
 
     /// Begins a new block, optionally inspecting the ABCI
     /// [`BeginBlock`](abci::request::BeginBlock) request.
@@ -31,9 +31,10 @@ pub trait Component {
     /// implementor MUST ensure that any clones of the `Arc` are dropped before
     /// it returns, so that `state.get_mut().is_some()` on completion.
     async fn begin_block<S: StateWrite + 'static>(
-        state: &mut Arc<S>,
-        begin_block: &abci::request::BeginBlock,
-    );
+        _state: &mut Arc<S>,
+        _begin_block: &abci::request::BeginBlock,
+    ) {
+    }
 
     /// Ends the block, optionally inspecting the ABCI
     /// [`EndBlock`](abci::request::EndBlock) request, and performing any batch
@@ -50,9 +51,10 @@ pub trait Component {
     /// implementor MUST ensure that any clones of the `Arc` are dropped before
     /// it returns, so that `state.get_mut().is_some()` on completion.
     async fn end_block<S: StateWrite + 'static>(
-        state: &mut Arc<S>,
-        end_block: &abci::request::EndBlock,
-    );
+        _state: &mut Arc<S>,
+        _end_block: &abci::request::EndBlock,
+    ) {
+    }
 
     /// Ends the epoch, applying component-specific state transitions that should occur when an epoch ends.
     ///
@@ -63,5 +65,7 @@ pub trait Component {
     /// called, `state.get_mut().is_some()`, i.e., the `Arc` is not shared.  The
     /// implementor MUST ensure that any clones of the `Arc` are dropped before
     /// it returns, so that `state.get_mut().is_some()` on completion.
-    async fn end_epoch<S: StateWrite + 'static>(state: &mut Arc<S>) -> Result<()>;
+    async fn end_epoch<S: StateWrite + 'static>(_state: &mut Arc<S>) -> Result<()> {
+        Ok(())
+    }
 }