Bump wasmtime to 0.31.0 (#10149)

* Bump `wasmtime` to 0.31.0

* Bump `itoa` to 0.4.8

* sc-executor-wasmtime: fix `SandboxContext::invoke` which I've broke

* sc-executor-wasmtime: cargo fmt

substrate/client/executor/wasmtime/src/host.rs

@@ -333,6 +333,7 @@ impl<'a, 'b, 'c, 'd> sandbox::SandboxContext for SandboxContext<'a, 'b, 'c, 'd>
 		state: u32,
 		func_idx: SupervisorFuncIndex,
 	) -> Result<i64> {
+		let mut ret_vals = [Val::null()];
 		let result = self.dispatch_thunk.call(
 			&mut self.host_context.caller,
 			&[
@@ -341,26 +342,16 @@ impl<'a, 'b, 'c, 'd> sandbox::SandboxContext for SandboxContext<'a, 'b, 'c, 'd>
 				Val::I32(state as i32),
 				Val::I32(usize::from(func_idx) as i32),
 			],
+			&mut ret_vals,
 		);
 
 		match result {
-			Ok(ret_vals) => {
-				let ret_val = if ret_vals.len() != 1 {
-					return Err(format!(
-						"Supervisor function returned {} results, expected 1",
-						ret_vals.len()
-					)
-					.into())
-				} else {
-					&ret_vals[0]
-				};
-
-				if let Some(ret_val) = ret_val.i64() {
+			Ok(()) =>
+				if let Some(ret_val) = ret_vals[0].i64() {
 					Ok(ret_val)
 				} else {
 					return Err("Supervisor function returned unexpected result!".into())
-				}
-			},
+				},
 			Err(err) => Err(err.to_string().into()),
 		}
 	}