Commit resync writes in one transaction

Each insert, delete and rescore update was its own commit to disk, so a
resync of about a thousand QSOs froze the window thread. LogStore has a
new Batch() scope that commits its writes together. ContestSession uses
it in AddRangeFromNetwork, ClearFromNetwork and Rescore.

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

src/Nonemm.Session/ContestSession.cs

@@ -128,9 +128,12 @@ public sealed class ContestSession
                 && q.TimestampUtc >= fromUtc
                 && q.TimestampUtc < fromUtc + length)
             .ToList();
-        foreach (Qso qso in gone)
+        using (store.Batch())
         {
-            store.Delete(qso.Id);
+            foreach (Qso qso in gone)
+            {
+                store.Delete(qso.Id);
+            }
         }
         if (gone.Count > 0)
         {
@@ -152,10 +155,13 @@ public sealed class ContestSession
     {
         Log.Rescore();
         int written = 0;
-        foreach (Qso qso in Log.Qsos.Where(q => q.TimestampUtc >= fromUtc))
+        using (store.Batch())
         {
-            store.Update(qso);
-            written++;
+            foreach (Qso qso in Log.Qsos.Where(q => q.TimestampUtc >= fromUtc))
+            {
+                store.Update(qso);
+                written++;
+            }
         }
         Changed?.Invoke(this, EventArgs.Empty);
         return written;
@@ -216,11 +222,14 @@ public sealed class ContestSession
     {
         HashSet<string> held = [.. Log.Qsos.Select(q => q.Id)];
         List<Qso> stored = [];
-        foreach (Qso qso in arriving)
+        using (store.Batch())
         {
-            if (held.Add(qso.Id))
+            foreach (Qso qso in arriving)
             {
-                stored.Add(store.Add(FromNetwork(qso)));
+                if (held.Add(qso.Id))
+                {
+                    stored.Add(store.Add(FromNetwork(qso)));
+                }
             }
         }
         if (stored.Count == 0)