fix: reduce task startup overhead and lazy-load notifications

shell/preload/sitecustomize.js

@@ -159,9 +159,13 @@ try {
 
   run();
 
-  const { sendNotify } = require('./__ql_notify__.js');
   global.QLAPI = {
-    notify: sendNotify,
+    notify(...args) {
+      // Keep notification dependencies out of ordinary script startup.
+      // require caches the module after the first notification.
+      const { sendNotify } = require('./__ql_notify__.js');
+      return sendNotify.apply(this, args);
+    },
     ...client,
   };
 } catch (error) {

shell/preload/sitecustomize.py

@@ -129,10 +129,12 @@ try:
 
     run()
 
-    from __ql_notify__ import send
-
     class BaseApi(Client):
         def notify(self, *args, **kwargs):
+            # Most scripts never send a notification. Python caches this
+            # module after the first call, including its channel dependencies.
+            from __ql_notify__ import send
+
             return send(*args, **kwargs)
 
     QLAPI = BaseApi()