build(nix): rust-overlay -> fenix

this fixes linking issues we're having with rust 1.80 and cross
compiling

flake.nix

@@ -4,9 +4,12 @@
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
 
-    rust-overlay = {
-      url = "github:oxalica/rust-overlay";
-      inputs.nixpkgs.follows = "nixpkgs";
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs = {
+        nixpkgs.follows = "nixpkgs";
+        rust-analyzer-src.follows = "";
+      };
     };
 
     treefmt-nix = {
@@ -19,7 +22,7 @@
     {
       self,
       nixpkgs,
-      rust-overlay,
+      fenix,
       treefmt-nix,
     }:
     let
@@ -84,7 +87,7 @@
 
           mkStatic = pkgs.callPackage ./nix/static.nix {
             inherit (packages') refraction;
-            rust-overlay = rust-overlay.packages.${system};
+            fenix = fenix.packages.${system};
           };
 
           containerize =

nix/static.nix

@@ -1,19 +1,21 @@
 {
   lib,
-  refraction,
-  rust-overlay,
   pkgsCross,
+  fenix,
+  refraction,
 }:
 let
   crossPlatformFor = with pkgsCross; {
     x86_64 = musl64.pkgsStatic;
     aarch64 = aarch64-multiplatform.pkgsStatic;
   };
 
-  toolchain = rust-overlay.rust.minimal.override {
-    extensions = [ "rust-std" ];
-    targets = lib.mapAttrsToList (_: pkgs: pkgs.stdenv.hostPlatform.rust.rustcTarget) crossPlatformFor;
-  };
+  toolchain = fenix.combine (
+    [ fenix.stable.minimalToolchain ]
+    ++ lib.mapAttrsToList (
+      _: pkgs: fenix.targets.${pkgs.stdenv.hostPlatform.rust.rustcTarget}.stable.rust-std
+    ) crossPlatformFor
+  );
 
   rustPlatformFor = lib.mapAttrs (
     _: pkgs: