fix(serve): support serve hmr (#26078)

This PR addresses issue #25600 

Changes:
Updated `fn has_hmr` to check `serve` subcommand and return its hmr
value if found, in order to run the worker in serve mode with
hmr_runner. Thus the hmr event can be dispatched upon changes on the
file served.

cli/args/mod.rs

@@ -1452,6 +1452,12 @@ impl CliOptions {
       watch: Some(WatchFlagsWithPaths { hmr, .. }),
       ..
     }) = &self.flags.subcommand
+    {
+      *hmr
+    } else if let DenoSubcommand::Serve(ServeFlags {
+      watch: Some(WatchFlagsWithPaths { hmr, .. }),
+      ..
+    }) = &self.flags.subcommand
     {
       *hmr
     } else {

cli/tools/serve.rs

@@ -44,12 +44,15 @@ pub async fn serve(
   maybe_npm_install(&factory).await?;
 
   let worker_factory = factory.create_cli_main_worker_factory().await?;
-
+  let hmr = serve_flags
+    .watch
+    .map(|watch_flags| watch_flags.hmr)
+    .unwrap_or(false);
   do_serve(
     worker_factory,
     main_module.clone(),
     serve_flags.worker_count,
-    false,
+    hmr,
   )
   .await
 }
@@ -109,8 +112,6 @@ async fn do_serve(
     }
   }
   Ok(exit_code)
-
-  // main.await?
 }
 
 async fn run_worker(
@@ -119,7 +120,7 @@ async fn run_worker(
   main_module: ModuleSpecifier,
   hmr: bool,
 ) -> Result<i32, AnyError> {
-  let mut worker = worker_factory
+  let mut worker: crate::worker::CliMainWorker = worker_factory
     .create_main_worker(
       deno_runtime::WorkerExecutionMode::Serve {
         is_main: false,