Move and batch spots the way N1MM does

Two differences from N1MM in the spot path, both found by reading Packet.cs.

Randomising moved every CW spot. PacketSpot.Randomize moves a spot only when it
is not a dupe, not a self spot, not on a CQ frequency, is on CW and is not
working split, and Packet skips it altogether for a station passed to another
band. Moving a dupe or a split station makes it harder to find, not easier, so
this now leaves the same ones alone. Whether a station has been worked comes
from the log, so AppSession asks it before moving a spot.

Split needed knowing where a station is listening, which is in the comment. Qsx
reads it by N1MM's rules: QSX, UP, DOWN, DN, U or D, the word standing alone or
after a space, a bare number after QSX meaning kilohertz inside the band and
anything else an offset from the spot, an offset over a hundred kilohertz
refused unless it says QSX, DN70 read as a grid square rather than five down,
and a listening frequency outside the band thrown away.

Spots reached the bandmap one at a time, each one redrawing every window that
watches it. N1MM queues them and flushes the queue once a second, which is what
this does now: the filters and the randomiser run over the batch, and the
bandmap takes it in one call and raises one change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Nonemm.Spotting/Bandmap.cs

@@ -43,6 +43,27 @@ public sealed class Bandmap
         Changed?.Invoke(this, EventArgs.Empty);
     }
 
+    /// A batch of spots in one go, so a busy node redraws the windows once
+    /// rather than once a spot. N1MM collects arriving spots the same way.
+    public void AddRange(IEnumerable<Spot> spots)
+    {
+        int added = 0;
+        lock (guard)
+        {
+            foreach (Spot spot in spots)
+            {
+                string key = Key(spot);
+                this.spots[key] = spot;
+                arrived[key] = clock();
+                added++;
+            }
+        }
+        if (added > 0)
+        {
+            Changed?.Invoke(this, EventArgs.Empty);
+        }
+    }
+
     public void Remove(Callsign call, Band band)
     {
         string key = $"{call.Text}|{band.Name}";