Set up shell.nix direnv

.envrc

@@ -0,0 +1 @@
+use nix

shell.nix

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+{ pkgs ? import <nixpkgs> {}}:
+
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    rustc
+    cargo
+    rustfmt
+    rust-analyzer
+    clippy
+
+    pkg-config
+    openssl
+  ];
+
+  RUST_BACKTRACE = 1;
+}