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

libraries/bezier-rs/src/subpath/lookup.rs

@@ -120,11 +120,10 @@ impl<ManipulatorGroupId: crate::Identifier> Subpath<ManipulatorGroupId> {
 
 #[cfg(test)]
 mod tests {
+	use super::*;
 	use crate::consts::MAX_ABSOLUTE_DIFFERENCE;
 	use crate::utils::f64_compare;
 
-	use super::*;
-
 	#[test]
 	fn length_quadratic() {
 		let start = DVec2::new(20., 30.);