Use nightly in flake.nix build derivations

flake.nix

@@ -26,6 +26,20 @@ Updating `cargoHash`:
       pkgs = import nixpkgs {
         inherit system overlays;
       };
+      # nightly is required for function signal syntax in leptos
+      # https://leptos-rs.github.io/leptos/02_getting_started.html
+      rust-bin = pkgs.rust-bin.nightly.latest.minimal;
+      rust-binWasm = rust-bin.override {
+        targets = [ "wasm32-unknown-unknown" ];
+      };
+      rustPlatform = pkgs.makeRustPlatform {
+        cargo = rust-bin;
+        rustc = rust-bin;
+      };
+      rustPlatformWasm = pkgs.makeRustPlatform {
+        cargo = rust-binWasm;
+        rustc = rust-binWasm;
+      };
       rustSettings = with pkgs; {
         src = ./.;
         cargoHash = nixpkgs.lib.fakeHash;
@@ -38,10 +52,7 @@ Updating `cargoHash`:
     in {
       devShells.${system}.default = with pkgs; mkShell {
         packages = [
-          # nightly is required for function signal syntax in leptos
-          # https://leptos-rs.github.io/leptos/02_getting_started.html
-          (pkgs.rust-bin.nightly.latest.default.override {
-            targets = [ "wasm32-unknown-unknown" ];
+          (rust-binWasm.override {
             extensions = [ "rust-src" ];
           })
           bacon
@@ -49,9 +60,8 @@ Updating `cargoHash`:
         inputsFrom = with self.packages.${system}; [ dyesub-tool dyesub-cli ];
       };
       packages.${system} = {
-        # TODO: use nightly
         default = self.packages.${system}.dyesub-cli;
-        dyesub-cli = pkgs.rustPlatform.buildRustPackage (rustSettings // {
+        dyesub-cli = rustPlatform.buildRustPackage (rustSettings // {
           pname = "dyesub-cli";
           version = "0.1.0";
           buildAndTestSubdir = "dyesub-cli";
@@ -60,7 +70,7 @@ Updating `cargoHash`:
             description = "A tool for generating dye sublimation transfer sheet SVGs for Japanese thumb shift 拇指シフト keycaps.";
           };
         });
-        dyesub-tool = pkgs.rustPlatform.buildRustPackage (rustSettings // {
+        dyesub-tool = rustPlatformWasm.buildRustPackage (rustSettings // {
           pname = "dyesub-tool";
           version = "0.1.0";
           buildAndTestSubdir = "dyesub-tool";