feat(nix): flake-parts, first draft

nix/shells/default.nix

@@ -0,0 +1,25 @@
+{ inputs, ... }:
+{
+  perSystem =
+    {
+      self',
+      lib,
+      pkgs,
+      ...
+    }:
+    let
+      uwulib = inputs.self.uwulib.init pkgs;
+    in
+    {
+      # basic nix shell containing all things necessary to build continuwuity in all flavors manually (on x86_64-linux)
+      devShells.default = uwulib.build.craneLib.devShell {
+        packages = [
+          pkgs.pkg-config
+          pkgs.liburing
+          self'.packages.rust-jemalloc-sys-unprefixed'
+          self'.packages.rocksdbAllFeatures
+        ];
+        env.LIBCLANG_PATH = lib.makeLibraryPath [ pkgs.llvmPackages.libclang.lib ];
+      };
+    };
+}