fix: add HasHiddenParent() to skip hidden command subtrees in Walk()

[dearchap]

What type of PR is this?

• feature

What this PR does / why we need it:

When using Walk() to traverse the command tree, users who want to skip hidden commands currently check cmd.Hidden. However, the subcommands of a hidden command are not themselves hidden and still appear in the walk output. There is no way to check whether a command belongs to a hidden subtree without manually walking parent pointers, which are unexported.

This PR adds HasHiddenParent() bool to Command, which returns true if any ancestor has Hidden: true. Users can combine it with cmd.Hidden in their Walk callback to skip entire hidden subtrees:

cmd.Walk(func(c *cli.Command) error {
    if c.Hidden || c.HasHiddenParent() {
        return nil
    }
    // process visible commands only
})

Which issue(s) this PR fixes:

Fixes #2372

Testing

• go test ./... passes
• go vet ./... passes
• make v3diff shows only the new HasHiddenParent method
• make v3approve run to update API surface docs

Release Notes

Add Command.HasHiddenParent() method to help users skip subcommands of hidden commands during Walk().