feat: init with rust lib and bin crate

templates/default/nix/lib/default.nix

@@ -0,0 +1,13 @@
+{ inputs, flake, ... }:
+
+{
+  mkCraneLib =
+    { pkgs, system }:
+    let
+      craneLib = inputs.crane.mkLib pkgs;
+      toolchain = (inputs.rust-overlay.lib.mkRustBin { } pkgs).fromRustupToolchainFile (
+        flake + "/rust-toolchain.toml"
+      );
+    in
+    craneLib.overrideToolchain toolchain;
+}