chore(nix): update nixfmt-rfc-style to nixfmt (#293)

The nixfmt-rfc-style package has been merged into nixfmt as of Nix 2.24.
RFC 166 formatting is now the default behaviour, making the separate
package unnecessary.

Author: ryoppippi

flake.nix

@@ -30,7 +30,7 @@
 
               # formatting and linting tools
               similarity
-              nixfmt-rfc-style
+              nixfmt
               tsgolint
               oxlint
               oxfmt