Allow updating position and mode on missing nodes (#6792)

When a node is missing, attempts to serialize it will return the "last
known good" serialization to ensure that the node will still be
functional in the future (the node pack is installed/comfyui is
updated). However, this means even small and safe changes (like moving
the node out of the way or bypassing it so the workflow can be run) will
be discarded on reload.

This is resolved by including the updated position and mode when
returning early.

| Before | After |
| ------ | ----- |
| <img width="360" height="360" alt="before"
src="https://github.com/user-attachments/assets/8452682c-9531-4153-a258-158c634df3e8"
/> | <img width="360" height="360" alt="after"
src="https://github.com/user-attachments/assets/8825ce5e-c4a6-4f4a-be20-97e4aca69964"
/> |

Thanks to @Kosinkadink for bringing this up

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6792-Allow-updating-position-and-mode-on-missing-nodes-2b26d73d365081ed8c22fafe5348c49f)
by [Unito](https://www.unito.io)

src/lib/litegraph/src/LGraphNode.ts

@@ -882,7 +882,7 @@ export class LGraphNode
 
     // special case for when there were errors
     if (this.constructor === LGraphNode && this.last_serialization)
-      return this.last_serialization
+      return { ...this.last_serialization, mode: o.mode, pos: o.pos }
 
     if (this.inputs)
       o.inputs = this.inputs.map((input) => inputAsSerialisable(input))