fix: make session saving asynchronous to improve picker close performance

Remove await from savePickerSession call in defer block to prevent blocking picker close.
Session save now happens in background with error handling.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: lambdalisue

denops/fall/main/picker.ts

@@ -212,15 +212,18 @@ async function startPicker<T extends Detail>(
   stack.defer(() => {
     zindex -= Picker.ZINDEX_ALLOCATION;
   });
-  stack.defer(async () => {
+  stack.defer(() => {
     const name = pickerParams.name;
     if (SESSION_EXCLUDE_SOURCES.includes(name)) {
       return;
     }
-    await savePickerSession({
+    // Save session asynchronously without blocking picker close
+    savePickerSession({
       name,
       args,
       context: itemPicker.context,
+    }).catch((error) => {
+      console.error(`Failed to save picker session: ${error}`);
     });
   });