feat(nix): flake-parts, first draft

nix/packages/uwulib/environment.nix

@@ -0,0 +1,18 @@
+args@{ pkgs, inputs, ... }:
+let
+  uwubuild = import ./build.nix args;
+in
+rec {
+  buildDepsOnlyEnv = {
+    # https://crane.dev/faq/rebuilds-bindgen.html
+    NIX_OUTPATH_USED_AS_RANDOM_SEED = "aaaaaaaaaa";
+    CARGO_PROFILE = "release";
+  }
+  // uwubuild.craneLib.mkCrossToolchainEnv (p: pkgs.clangStdenv);
+
+  buildPackageEnv = {
+    GIT_COMMIT_HASH = inputs.self.rev or inputs.self.dirtyRev or "";
+    GIT_COMMIT_HASH_SHORT = inputs.self.shortRev or inputs.self.dirtyShortRev or "";
+  }
+  // buildDepsOnlyEnv;
+}