Obviate leptosfmt wrapper

[srid]

https://github.com/bram209/leptosfmt/releases/tag/0.1.13 is released with the two necessary changes that will allow us to finally get rid of this wrapper.

treefmt-nix/programs/leptosfmt.nix

Lines 26 to 41 in 843e1e1

	command = pkgs.writeShellApplication {
	name = "leptosfmt-forall";
	runtimeInputs = [
	cfg.package
	modify-unless-unchanged
	];
	text = ''
	# leptosfmt doesn't take multiple arguments yet
	# https://github.com/bram209/leptosfmt/issues/63
	for file in "$@"; do
	# Use the modify-unless-unchanged hack until this is implemented:
	# https://github.com/bram209/leptosfmt/issues/64
	modify-unless-unchanged leptosfmt "$file"
	done
	'';
	};

• Upstream 0.1.13 to nixpkgs
• Use that in this module (should we still keep the wrapper for older versions, or require user to use newer nixpkgs?)