Add option `--fmt` or `--format` which outputs the result to stdout

Hello, I want to add `deadnix` to my `dprint` configuration, the problem that `dprint` requires that the command outputs the result to stdout and not change the file directly.
Already `deadnix` generates the output through the `--edit` command, but I want it to print it out.

Start at the CLI entry point and locate the existing --edit option and the code that generates formatted output. Add the requested stdout mode without changing files, then verify that the result is printed to stdout and that the existing --edit behavior remains unchanged.

Written by the indexing model from the issue text.