[thde]

cmd.Run already took stdin, stdout and stderr, but commands didn't use them consistently. Some wrote to os.Stderr directly. Warnings, spinners and prompts were mixed into stdout, which broke the JSON from nctl get all -o json and hid prompts when stdout was redirected. Exec subprocesses checked the process's stdin for a terminal instead of the command's. The streams were also bound as a loose io.Writer and io.Reader next to Kong's own writers, so stdout had two sources and a hook couldn't tell which stream it had been given.

This PR introduces a single value that carries a command's streams (a pattern also used by kubectl):

// IOStreams are the standard input, output and error of a command.
type IOStreams struct {
        In     io.Reader // input commands prompt from
        Out    io.Writer // output of a command
        ErrOut io.Writer // diagnostics, see Writer.Err
}

Run builds it once and newParser binds it for the BeforeApply hooks of format.Writer and format.Reader. It also makes those streams Kong's writers, so help text, parse errors and command output share one source. format no longer imports Kong. Writer gains Err() for diagnostics and Out()/In() for the raw streams, so terminal detection and subprocess inheritance keep working. In tests, testutil.KongStreams replaces the hand-built KongContext.

Behaviour changes

Warnings, spinners, confirmation prompts and Run's own errors now go to stderr, and usage output stays on stdout. Scripts that read warnings or errors from stdout need to read stderr instead. main now gets its streams from moby/term.StdStreams(), so on Windows every command runs with virtual terminal sequences enabled.