plugins/rustaceanvim: move source files to languages/rust subfolder

plugins/default.nix

@@ -69,7 +69,7 @@
     ./languages/python/jupytext.nix
     ./languages/qmk.nix
     ./languages/rust/rust-tools.nix
-    ./languages/rustaceanvim.nix
+    ./languages/rust/rustaceanvim.nix
     ./languages/sniprun.nix
     ./languages/tagbar.nix
     ./languages/texpresso.nix

plugins/languages/rust/rustaceanvim.nix

@@ -175,7 +175,7 @@ in
 
       settings =
         helpers.mkNullOrStrLuaFnOr
-          (types.submodule { options = import ../lsp/language-servers/rust-analyzer-config.nix lib pkgs; })
+          (types.submodule { options = import ../../lsp/language-servers/rust-analyzer-config.nix lib pkgs; })
           ''
             Setting passed to rust-analyzer.
             Defaults to a function that looks for a `rust-analyzer.json` file or returns an empty table.