feat(crimp): Add Nix build for crate

... mostly to get CI.

Note that this adds the Cargo.lock file because we require pinning,
but it is generally not required for Rust libraries.

Change-Id: I565c7c8e899694accf3efd825ff46225f3c47d1a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3363
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

net/crimp/default.nix

@@ -0,0 +1,9 @@
+{ depot, pkgs, ... }:
+
+depot.third_party.naersk.buildPackage {
+  src = ./.;
+  buildInputs = with pkgs; [
+    openssl
+    pkgconfig
+  ];
+}