chore: build aiken package directly

When you build it currently, most of the code is kept on the final
derivation. Building it manually makes sure that only the binaries are
there.

flake.nix

@@ -29,12 +29,17 @@
 
           buildInputs = with pkgs; [ openssl ] ++ osxDependencies;
           nativeBuildInputs = with pkgs; [ pkg-config openssl.dev ];
-          cargoBuildFlags = [ "--package aiken" ];
+          cargoBuildFlags = [ "-p aiken" ];
 
           src = pkgs.lib.cleanSourceWith { src = self; };
 
           cargoLock.lockFile = ./Cargo.lock;
 
+          installPhase = ''
+            mkdir -p $out/bin
+            cp target/release/aiken $out/bin
+          '';
+
           meta = with pkgs.lib; {
             description = "Cardano smart contract language and toolchain";
             homepage = "https://github.com/aiken-lang/aiken";