Prevent subcommand from inheriting flags/options from parent?

I see that when a subcommand's help text is generated, it's based on a stack, which eventually includes its ancestor's flags/options, etc. So the following definition

```swift
struct Math: ParsableCommand {
static var configuration = CommandConfiguration(subcommands: [Add.self])

@Flag()
var version: Bool
}

extension Math {
struct Add: ParsableCommand {}
}
```

means the help text for `add` will be the following:

```
USAGE: math add

OPTIONS:
--version
-h, --help Show help information.
```

There should be a way to prevent `--version` to be included here IMO.

Start by tracing how subcommand help text is generated and how the ancestor flags/options are collected on the stack. Confirm the behavior with the Math and Add example, then determine a way for a subcommand to exclude inherited options. Done means `math add --help` no longer lists the parent’s `--version` flag while retaining the subcommand’s own help option.

Written by the indexing model from the issue text.