fix: exit build.dart early on Linux builds so we can use the package on a Linux host

thermion_dart/hook/build.dart

@@ -22,6 +22,14 @@ void main(List<String> args) async {
 
     var platform = config.targetOS.toString().toLowerCase();
 
+    // We don't support Linux (yet), so the native/Filament libraries won't be 
+    // compiled/available. However, we still want to be able to run the Dart 
+    // package itself on a Linux host(e.g. for dart_services backed), so if 
+    // we detect that we're running on Linux, just exit here.
+    if (platform == "linux") {
+      return;
+    }
+
     var libDir = config.dryRun ? "" : (await getLibDir(config, logger)).path;
 
     final packageName = config.packageName;