rnix removed because it is unmaintained

[pigeonhands]

Currently, editing a nix file gives an error about rnix being unmaintained

[ERROR][2024-08-30 13:12:42] .../vim/lsp/rpc.lua:770	"rpc"	"nix-shell"	"stderr"	"error:\n       
… while calling the 'derivationStrict' builtin\n\n         at /builtin/derivation.nix:9:12: (source not available)\n\n       
… while evaluating derivation 'shell'\n         whose name attribute is located at /nix/store/5z81la6av4j0ckp0w1949lxiwjyyykks-source/pkgs/stdenv/generic/make-derivation.nix:333:7\n\n       
… while evaluating attribute 'buildInputs' of derivation 'shell'\n\n         at /nix/store/5z81la6av4j0ckp0w1949lxiwjyyykks-source/pkgs/stdenv/generic/make-derivation.nix:380:7:\n\n          379|       depsHostHost                = elemAt (elemAt dependencies 1) 0;\n          380|       buildInputs                 = elemAt (elemAt dependencies 1) 1;\n             |       ^\n          381|       depsTargetTarget            = elemAt (elemAt dependencies 2) 0;\n\n       
error: 'rnix-lsp' has been removed as it is unmaintained\n"

Also means formatting does not work currently. Is there a way to manually specify a lsp/formatter and completely override preferred_servers? nixfmt may be a replacement.