Feature request: Add --no-{flag_name}

[parasyte]

This was requested privately. The idea is to invert the value of argument flags (fields with bool value) when it defaults to true.

E.g. This would be valid and would parse --no-recurse to args.recurse == false:

#[derive(OnlyArgs)]
struct Args {
    #[default(true)]
    recurse: bool,
}

Meanwhile, if #[default(true)] is not used on the flag, then --no-recurse would be an argument parser error; only --recurse would be allowed.

Without this feature, there is no way to turn off default flags.

Potential caveats

This feature could lead to some weird ambiguities. For instance:

#[derive(OnlyArgs)]
struct Args {
    #[default(true)]
    recurse: bool,

    no_recurse: bool,
}

This cli supports two explicit flags: --recurse and --no-recurse for both struct fields, plus one implicit flag, which is also --no-recurse (on the recurse field).

These ambiguities should probably end up as compile errors.