chore: build aiken package directly

When you build the application currently, it builds all crates and
exposes most of the directory inside of it, as well as not adding the
binary to the `$PATH`.

The `buildAndTestSubdir` flag for `buildRustPackage` fix this. It is not
documented anywhere, but it works...

flake.nix

@@ -29,12 +29,46 @@
 
           buildInputs = with pkgs; [ openssl ] ++ osxDependencies;
           nativeBuildInputs = with pkgs; [ pkg-config openssl.dev ];
-          cargoBuildFlags = [ "--package aiken" ];
 
-          src = pkgs.lib.cleanSourceWith { src = self; };
+          src = with pkgs;
+            lib.cleanSourceWith {
+              filter = orig_path: type:
+                let
+                  path = (toString orig_path);
+                  base = baseNameOf path;
+                  parentDir = baseNameOf (dirOf path);
+
+                  matchesSuffix = lib.any (suffix: lib.hasSuffix suffix base) [
+                    ".rs"
+                    ".toml"
+                  ];
+
+                  # Cargo.toml already captured above
+                  isCargoFile = base == "Cargo.lock";
+
+                  # .cargo/config.toml already captured above
+                  isCargoConfig = parentDir == ".cargo" && base == "config";
+                in type == "directory" || matchesSuffix || isCargoFile
+                || isCargoConfig;
+              src = ./.;
+            };
+
+          # Tests might be impure and we shouldn't need to run them.
+          doCheck = false;
 
           cargoLock.lockFile = ./Cargo.lock;
 
+          buildPhase = ''
+            cargo build --release
+          '';
+
+          installPhase = ''
+            find . -type f ! -executable -name "aiken" -delete
+
+            mkdir -p $out/bin
+            install -Dm755 target/release/aiken $out/bin
+          '';
+
           meta = with pkgs.lib; {
             description = "Cardano smart contract language and toolchain";
             homepage = "https://github.com/aiken-lang/aiken";