Cut CPU use and move heavy work off the UI thread

Redraws:
- Merge bursts of session and bandmap events into one redraw
  (Coalesced). Closed Bandmap and Available windows now unsubscribe.
- Grayline and Voice Keyer no longer subscribe to the session twice.
- Available summary, Score table and Log rows redraw only when their
  contents change. Telnet lines are added in batches.
- Bandmap view reuses its layout, shaped text and brushes. Grayline
  draws the coastlines as one cached shape.

Threads:
- Available, Bandmap colours, Check and Statistics do their judging
  and counting on the thread pool and draw the result on the UI thread.
- ContestLog takes a lock in Judge and in each method that changes the
  log, so a background Judge cannot read the indexes mid-edit.

Refresh rate:
- Statistics refreshes every 30 seconds and when the QSO count changes.
- Grayline refreshes at most every 15 seconds on session events.

Publish with ReadyToRun to cut startup JIT time.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Nonemm.App/Windows/BandmapView.cs

@@ -99,14 +99,35 @@ public sealed class BandmapView : Control
         DrawSegments(context);
         DrawScale(context, ink);
         DrawVfos(context);
-        placed = [.. BandmapLayout.Place(Spots, scale, LabelHeight)
-            .Select(l => l with { MarkY = l.MarkY + Inset, LabelY = l.LabelY + Inset })];
+        PlaceLabels();
         foreach (BandmapLabel label in placed)
         {
             DrawLabel(context, label, ink);
         }
     }
 
+    private IReadOnlyList<Spot> placedSpots = [];
+    private BandmapScale? placedScale;
+    private double placedHeight;
+
+    /// Lays the callsigns out again only when the spots, the scale or the text
+    /// size are not what the last layout used. Redraws for any other reason, a
+    /// moving receiver bar for one, reuse it.
+    private void PlaceLabels()
+    {
+        if (placedScale == scale
+            && placedHeight == LabelHeight
+            && (ReferenceEquals(placedSpots, Spots) || placedSpots.SequenceEqual(Spots)))
+        {
+            return;
+        }
+        placedSpots = Spots;
+        placedScale = scale;
+        placedHeight = LabelHeight;
+        placed = [.. BandmapLayout.Place(Spots, scale, LabelHeight)
+            .Select(l => l with { MarkY = l.MarkY + Inset, LabelY = l.LabelY + Inset })];
+    }
+
     /// N1MM paints the CW, digital and phone parts of the band behind the
     /// scale, the digital block over the other two.
     /// Anything past a band edge is painted as out of band, which is the only
@@ -209,12 +230,20 @@ public sealed class BandmapView : Control
     protected override void OnPointerMoved(PointerEventArgs e)
     {
         base.OnPointerMoved(e);
+        Spot? under = LabelAt(e.GetPosition(this))?.Spot;
+        if (Equals(under, tipFor))
+        {
+            return;
+        }
+        tipFor = under;
         ToolTip.SetShowDelay(this, 0);
-        ToolTip.SetTip(
-            this,
-            LabelAt(e.GetPosition(this)) is { } label ? SpotDescription.Of(label.Spot) : null);
+        ToolTip.SetTip(this, under is null ? null : SpotDescription.Of(under));
     }
 
+    /// The spot the tool tip describes, so moving the pointer along a callsign
+    /// does not build the text again.
+    private Spot? tipFor;
+
     protected override void OnPointerPressed(PointerPressedEventArgs e)
     {
         base.OnPointerPressed(e);
@@ -227,23 +256,56 @@ public sealed class BandmapView : Control
         FrequencyPicked?.Invoke(this, scale.At(at.Y - Inset));
     }
 
-    private FormattedText Text(string text, IBrush brush, double size, bool bold = false, bool italic = false) =>
-        new(
+    /// Shaping text is the dearest part of a redraw, and the same few hundred
+    /// callsigns and frequency numbers are drawn every time, so each is kept.
+    private readonly Dictionary<(string Text, IBrush Brush, double Size, bool Bold, bool Italic), FormattedText> texts = [];
+
+    private FormattedText Text(string text, IBrush brush, double size, bool bold = false, bool italic = false)
+    {
+        if (texts.TryGetValue((text, brush, size, bold, italic), out FormattedText? kept))
+        {
+            return kept;
+        }
+        if (texts.Count > 2000)
+        {
+            texts.Clear();
+        }
+        FormattedText made = new(
             text,
             CultureInfo.InvariantCulture,
             FlowDirection.LeftToRight,
             bold ? boldTypeface : italic ? italicTypeface : typeface,
             size,
             brush);
+        texts[(text, brush, size, bold, italic)] = made;
+        return made;
+    }
 
     /// The form's text colour, which the theme sets in both light and dark.
     private IBrush Foreground() =>
         this.FindResource("FormForeground") as IBrush ?? Brushes.Gray;
 
-    private static IBrush Opaque(IBrush ink, double opacity) =>
-        ink is ISolidColorBrush solid
-            ? new SolidColorBrush(solid.Color, opacity)
-            : ink;
+    private readonly Dictionary<(IBrush Ink, double Opacity), IBrush> faded = [];
+
+    /// Kept, so the same brush comes back each time and the text drawn with it
+    /// is found in `texts`.
+    private IBrush Opaque(IBrush ink, double opacity)
+    {
+        if (ink is not ISolidColorBrush solid)
+        {
+            return ink;
+        }
+        if (!faded.TryGetValue((ink, opacity), out IBrush? brush))
+        {
+            if (faded.Count > 50)
+            {
+                faded.Clear();
+            }
+            brush = new SolidColorBrush(solid.Color, opacity);
+            faded[(ink, opacity)] = brush;
+        }
+        return brush;
+    }
 
     private static IBrush BrushFor(VfoRole role) => role switch
     {