Extract the ssh debug commands into a transport neutral commands package (#1958)

Migrate commands from ssh into a transport neutral package

 - add golden tests validating that output remains unchanged
 - move commands to commands.go

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

commands/command.go

@@ -0,0 +1,60 @@
+package commands
+
+import (
+	"flag"
+)
+
+// CommandFlags is called before help or command execution to parse command line flags.
+// It should return a flag.FlagSet instance and a pointer to the struct that will contain parsed flags
+type CommandFlags func() (*flag.FlagSet, any)
+
+// CommandCallback is called when your command should execute.
+// fs will be a a pointer to the struct provided by Command.Flags callback, if there was one. -h and -help are reserved
+// and handled automatically for you.
+// a will be any unconsumed arguments, if no Command.Flags was available this will be all the flags passed in.
+// w is the writer to use when sending messages back to the client.
+// If an error is returned by the callback it is logged locally, the callback should handle messaging errors to the user
+// where appropriate
+type CommandCallback func(fs any, a []string, w StringWriter) error
+
+type Command struct {
+	Name             Name
+	ShortDescription string
+	Help             string
+
+	Flags    CommandFlags
+	Callback CommandCallback
+}
+
+func execCommand(c *Command, args []string, w StringWriter) error {
+	var (
+		fl *flag.FlagSet
+		fs any
+	)
+
+	if c.Flags != nil {
+		fl, fs = c.Flags()
+		if fl != nil {
+			// SetOutput() here in case fl.Parse dumps usage.
+			fl.SetOutput(w.GetWriter())
+			err := fl.Parse(args)
+			if err != nil {
+				// fl.Parse has dumped error information to the user via the w writer.
+				return err
+			}
+			args = fl.Args()
+		}
+	}
+
+	return c.Callback(fs, args, w)
+}
+
+func checkHelpArgs(args []string) bool {
+	for _, a := range args {
+		if a == "-h" || a == "-help" {
+			return true
+		}
+	}
+
+	return false
+}