Keep an excluded contact out of the score the way N1MM does

Three things were wrong with a contact the operator takes out of the claimed
score. The decompiled reference gives the rule in four places:

- `Contest.cs:437` returns zero points when `IsClaimedQso` is 0.
- `ContestInstance.cs:307` builds the where clause `CLAIMEDQSO = 1`, which the
  dupe search (`DBSupport.cs:1189`) and the multiplier search
  (`DBSupport.cs:1327`) both use, so an unclaimed contact takes nothing away
  from a later one.
- The score query (`DBSupport.cs:1807`) adds `ContactType <> 'D'`, which the
  other two do not. A contact marked as a dupe is therefore still searched for
  dupes and multipliers, and is left out of the score alone.
- `Contact.cs:1563`, `3307` and `3881` write `X-QSO:` rather than dropping the
  contact from the Cabrillo file.

`ContestLog` scored an unclaimed contact in full, and the Cabrillo writer left
it out of the file. `Qso.IsInScore` now holds the score rule and
`StatisticsPivot` uses it instead of its own copy.

The same reference also fixes the sent serial in three Cabrillo exporters.
ARRL 10M, Ukrainian DX and YO DX HF formatted the sent exchange from the
station rather than the contact, so a DX entrant exported `001` on every line.
N1MM reads the contact's own number: `CArrl10m.cs:122` writes it unpadded,
`CUkrainian.cs:232` and `CYOHFDX.cs:167` pad it to three digits.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015NZkFxHde1iifAQemFTHxf

src/Nonemm.Contests/Rules/YoDxHf.cs

@@ -55,6 +55,13 @@ public sealed class YoDxHf : Contest
 
     public string SentExchangeFor(StationInfo me) => me.CountryPrefix == "YO" ? me.County : "001";
 
+    /// What went out on this contact. A YO station sends the same county
+    /// every time; everyone else sends a serial, so the Cabrillo file reads the
+    /// contact's own number and not the first one. N1MM pads it to three
+    /// digits.
+    private string SentExchangeOn(Qso qso, StationInfo me) =>
+        me.CountryPrefix == "YO" ? me.County : $"{qso.SentNumber:000}";
+
     public int PointsFor(QsoContext qso)
     {
         if (qso.CountryPrefix == "YO")
@@ -88,7 +95,7 @@ public sealed class YoDxHf : Contest
             [
                 new CabrilloField(me.Callsign, 13),
                 new CabrilloField(qso.SentReport, 3),
-                new CabrilloField(SentExchangeFor(me), 6),
+                new CabrilloField(SentExchangeOn(qso, me), 6),
             ],
             [
                 new CabrilloField(qso.Call.Text, 13),