Add a '--dry-run' option

[adam-gaia]

Is your feature request related to a problem? Please describe.

I would like a way to see what files are passed to each formatter, without invoking the formatters.

Describe the solution you'd like

I propose adding a '--dry-run` flag that configures treefmt to print out something like

$ treefmt --dry-run
[dryrun] would execute /path/to/rustfmt src/main.rs src/lib.rs 
[dryrun] would execute /path/to/jsonfmt data.json
[dryrun] would execute /path/to/nixfmt flake.nix

without actually running any of the formatters.

I'm not particular on exactly how the messages look, so long as they contain the command that would have been invoked, with all its arguments.

Describe alternatives you've considered

treefmt -vv: I understand that I can get this info by enabling the verbose output, however, I'd really appreciate a way to get this info without actually running the formatters.

Additional context

Here's the background on why I really want this:

I ran into an issue while running treefmt where some binary files were getting "formatted" accidentally. It took me a while to debug because the contents of the binary files were getting printed to my terminal, making it impossible to scroll back and see the debug logs. I could have quickly figured out what was going on if treefmt had a --dry-run option as described. (longer version: https://github.com/numtide/treefmt/issues/198#issuecomment-2781969457)

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Thanks for the great tool btw!