feat(hydroflow_plus): add API for external network inputs (#1449)

This is a key step towards being able to unit-test HF+ graphs, by being
able to have controlled inputs. Outputs next.

hydro_deploy/core/src/deployment.rs

@@ -69,11 +69,29 @@ impl Deployment {
         Ok(())
     }
 
+    /// Runs `start()`, waits for the trigger future, then runs `stop()`.
+    /// This is useful if you need to initiate external network connections between
+    /// `deploy()` and `start()`.
+    pub async fn start_until(&mut self, trigger: impl Future<Output = ()>) -> Result<()> {
+        // TODO(mingwei): should `trigger` interrupt `deploy()` and `start()`? If so make sure shutdown works as expected.
+        self.start().await?;
+        trigger.await;
+        self.stop().await?;
+        Ok(())
+    }
+
     /// Runs `deploy()`, and `start()`, waits for CTRL+C, then runs `stop()`.
     pub async fn run_ctrl_c(&mut self) -> Result<()> {
         self.run_until(tokio::signal::ctrl_c().map(|_| ())).await
     }
 
+    /// Runs `start()`, waits for CTRL+C, then runs `stop()`.
+    /// This is useful if you need to initiate external network connections between
+    /// `deploy()` and `start()`.
+    pub async fn start_ctrl_c(&mut self) -> Result<()> {
+        self.start_until(tokio::signal::ctrl_c().map(|_| ())).await
+    }
+
     pub async fn deploy(&mut self) -> Result<()> {
         self.services.retain(|weak| weak.strong_count() > 0);