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/gstd/src/any.rs

@@ -265,6 +265,7 @@ impl<I, O> PanicNode<I, O> {
 #[cfg(test)]
 mod test {
 	use super::*;
+
 	use graphene_core::{ops::AddPairNode, ops::IdentityNode};
 
 	#[test]

node-graph/gstd/src/image_color_palette.rs

@@ -62,10 +62,10 @@ fn image_color_palette(frame: ImageFrame<Color>, max_size: u32) -> Vec<Color> {
 
 #[cfg(test)]
 mod test {
-	use graphene_core::{raster::Image, value::CopiedNode};
-
 	use super::*;
 
+	use graphene_core::{raster::Image, value::CopiedNode};
+
 	#[test]
 	fn test_image_color_palette() {
 		assert_eq!(