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>

tests/Nonemm.Spotting.Tests/QsxTests.cs

@@ -0,0 +1,60 @@
+using Nonemm.Core;
+
+namespace Nonemm.Spotting.Tests;
+
+public class QsxTests
+{
+    private static readonly Frequency Spot = Frequency.FromKilohertz(14_025);
+
+    private static double Kilohertz(string comment) => Qsx.Parse(comment, Spot).Kilohertz;
+
+    [Fact]
+    public void AWholeFrequencyAfterQsxIsTakenAsItIs() =>
+        Assert.Equal(14_205, Kilohertz("QSX 14205"));
+
+    [Fact]
+    public void ABareNumberAfterQsxIsKilohertzInTheBand() =>
+        Assert.Equal(14_205, Kilohertz("QSX 205"));
+
+    [Fact]
+    public void UpAndDownAreOffsetsFromTheSpot()
+    {
+        Assert.Equal(14_027, Kilohertz("UP 2"));
+        Assert.Equal(14_020, Kilohertz("DN 5"));
+        Assert.Equal(14_020, Kilohertz("DOWN 5"));
+    }
+
+    [Fact]
+    public void ACommentThatSaysNothingAboutSplitGivesNothing()
+    {
+        Assert.Equal(0, Kilohertz("CQ TEST"));
+        Assert.Equal(0, Kilohertz(""));
+    }
+
+    [Fact]
+    public void AGridSquareIsNotAnOffset() =>
+        Assert.Equal(0, Kilohertz("TNX QSO DN70"));
+
+    [Fact]
+    public void AWordThatOnlyHoldsTheLettersIsNotAnOffset() =>
+        Assert.Equal(0, Kilohertz("GROUP 5"));
+
+    [Fact]
+    public void ABigNumberAfterAnythingButQsxIsNotAnOffset() =>
+        Assert.Equal(0, Kilohertz("UP 14205"));
+
+    [Fact]
+    public void AListeningFrequencyOutsideTheBandIsDropped() =>
+        Assert.Equal(0, Kilohertz("QSX 7205"));
+
+    [Fact]
+    public void TheSpotLineCarriesTheListeningFrequency()
+    {
+        Spot? spot = SpotLine.Parse(
+            "DX de W3LPL:     14025.0  JA1XYZ       UP 2                   1234Z",
+            new DateTime(2026, 8, 28, 12, 0, 0, DateTimeKind.Utc));
+
+        Assert.Equal(14_027_000, Assert.IsType<Spot>(spot).Qsx.Hertz);
+        Assert.True(spot.IsSplit);
+    }
+}