chore: reorganize nix files

nix/packages/default.nix

@@ -1,14 +1,16 @@
 {
   imports = [
     ./continuwuity
-    ./rocksdb
     ./rust.nix
     ./uwulib
   ];
 
   perSystem =
-    { self', ... }:
+    { self', pkgs, ... }:
     {
-      packages.default = self'.packages.continuwuity-default-bin;
+      packages = {
+        default = self'.packages.continuwuity-default-bin;
+        rocksdb = pkgs.callPackage ./rocksdb.nix { };
+      };
     };
 }

nix/packages/rocksdb/default.nix

@@ -1,12 +0,0 @@
-{
-  perSystem =
-    {
-      pkgs,
-      ...
-    }:
-    {
-      packages = {
-        rocksdb = pkgs.callPackage ./package.nix { };
-      };
-    };
-}

nix/packages/rust.nix

@@ -1,32 +0,0 @@
-{ inputs, ... }:
-{
-  perSystem =
-    {
-      system,
-      lib,
-      ...
-    }:
-    {
-      packages =
-        let
-          fnx = inputs.fenix.packages.${system};
-
-          stable = fnx.fromToolchainFile {
-            file = inputs.self + "/rust-toolchain.toml";
-
-            # See also `rust-toolchain.toml`
-            sha256 = "sha256-sqSWJDUxc+zaz1nBWMAJKTAGBuGWP25GCftIOlCEAtA=";
-          };
-        in
-        {
-          # used for building nix stuff (doesn't include rustfmt overhead)
-          build-toolchain = stable;
-          # used for dev shells
-          dev-toolchain = fnx.combine [
-            stable
-            # use the nightly rustfmt because we use nightly features
-            fnx.complete.rustfmt
-          ];
-        };
-    };
-}