Code cleanup and refactoring to enhance consistency (#1695)

- Move message handler payload data into structs
- Organize the file structure used by `editor/src/messages/portfolio/document` `/node_graph` and `/graph_operation`
- Make derive attributes use `serde::Serialize, serde::Deserialize` consistently instead of `use serde::{Deserialize, Serialize};` imports
- Various other code cleanup and refactoring

node-graph/gcore/src/uuid.rs

@@ -1,7 +1,6 @@
 use dyn_any::{DynAny, StaticType};
-use serde::{Deserialize, Serialize};
 
-#[derive(Clone, Copy, Serialize, Deserialize, specta::Type)]
+#[derive(Clone, Copy, serde::Serialize, serde::Deserialize, specta::Type)]
 pub struct Uuid(
 	#[serde(with = "u64_string")]
 	#[specta(type = String)]