fix: the FTDX10 refuses KY; — stop waiting on a status it will never send

The log settled it: the rig answers "?;" — its "unknown command" — to KY; and to
MG;. So the keyer status query cannot work on this model, and every send spent
four seconds waiting for an answer that was never coming.

"?;" is now recognised as what it is. A command refused once is never asked
again: models implement different subsets, and re-asking costs a 600 ms timeout
on every slow beat for a control that will never answer — which is also why the
panel felt sluggish.

Without a buffer status there is still a real constraint: one KY command carries
24 characters and the rig DROPS the rest silently. So the send is now paced by
how long the text takes to key, from PARIS timing at the rig's own speed. A long
macro goes out complete instead of losing its tail.

That leaves the question the log cannot answer: whether KY <text>; itself is
accepted. If the rig also replies "?;" to it, the CAT menu's PC KEYING setting is
the next suspect — but nothing in the code will be guessing at it.

internal/cat/yaesu_panel.go

@@ -17,6 +17,7 @@ package cat
 // rather than showing a zero that reads as "it reset itself".
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -199,8 +200,21 @@ func (y *Yaesu) readPanelSettings() {
 // this model lacks then keeps its previous value instead of dropping to zero,
 // which would look like a setting that reset itself.
 func (y *Yaesu) askNum(cmd, prefix string, digits int) (int, bool) {
+	// A command this model refused once is never asked again. Models implement
+	// different subsets — an FTDX10 answers "?;" to MG; — and re-asking costs a
+	// 600 ms timeout on every slow beat, for a control that will never answer.
+	if y.unsupported[cmd] {
+		return 0, false
+	}
 	r, err := y.ask(cmd)
 	if err != nil {
+		if errors.Is(err, errYaesuUnsupported) {
+			if y.unsupported == nil {
+				y.unsupported = map[string]bool{}
+			}
+			y.unsupported[cmd] = true
+			debugLog.Printf("yaesu: this rig does not support %q — not asking again", cmd)
+		}
 		return 0, false
 	}
 	if !strings.HasPrefix(r, prefix) || len(r) < len(prefix)+digits {