Keep the Check window's lists and columns between key presses

Tracing key presses with a busy feed showed the Check window rebuilding
the distinct call lists of the log, the call history and every spot,
and all five columns of controls, on each press.

- ContestLog.Revision goes up with every change to the contacts. The
  Check sources keep each call list until its source changes.
- The Check window builds a column again only when what it shows
  differs.

UI thread time while typing with eight windows open went from 14.6% to
9.3%.

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

src/Nonemm.Contests/ContestLog.cs

@@ -50,6 +50,10 @@ public sealed class ContestLog
 
     public Contest Contest => contest;
 
+    /// Goes up with every change to the contacts, so something worked out
+    /// from the log can be kept until this changes.
+    public int Revision { get; private set; }
+
     public IReadOnlyList<Qso> Qsos => qsos;
 
     /// The contacts alone. In WAE the log also holds QTC traffic, and a QTC
@@ -123,6 +127,7 @@ public sealed class ContestLog
             Qso scored = ApplyVerdict(qso, verdict);
             qsos.Add(scored);
             Index(scored, verdict);
+            Revision++;
             return scored;
         }
     }
@@ -342,6 +347,7 @@ public sealed class ContestLog
 
     private void Rebuild()
     {
+        Revision++;
         workedKeys.Clear();
         trafficWith.Clear();
         claimedMultipliers.Clear();