Lay out a Cabrillo line the way a .udc file asks for it

`CabrilloString` names a field and a column width in turn. The line it makes
follows N1MM: the operator's callsign in the first 13 columns, then every
column padded to its width with one space after it, and a value longer than its
column cut rather than pushed sideways. The cut is new for every contest, not
just the user-defined ones — the columns are the sponsor's, not ours.

`CabrilloVersion` is read too, so a contest whose sponsor still asks for 2.0
gets it in the header.

A contest that lays out its own line can put the transmitter column where it
wants it, or leave it out, so the writer no longer adds one at the end.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

tests/Nonemm.Formats.Tests/CabrilloWriterTests.cs

@@ -1,4 +1,6 @@
+using Nonemm.Contests;
 using Nonemm.Contests.Rules;
+using Nonemm.Contests.Udc;
 using Nonemm.Core;
 using Nonemm.Formats.Cabrillo;
 
@@ -80,4 +82,56 @@ public class CabrilloWriterTests
             [Contact() with { IsClaimed = false }]);
         Assert.DoesNotContain("QSO:", log);
     }
+
+    /// The SA 10 file, whose sponsor asks for its own columns: the operator's
+    /// call in the first 13, then every column padded to the width the file
+    /// gives, with one space after it.
+    [Fact]
+    public void AUserDefinedContestCanLayOutItsOwnLine()
+    {
+        UserDefinedContest contest = new(UdcFile.Parse("""
+            [Contest]
+            Name=SA10_DX
+            CabrilloName=SA10-DX
+            CabrilloFormat=99
+            CabrilloString=SNT, 4, SentExch, 4, CallSign, 13, RCV, 4, Exchange1, 4
+            """));
+        CabrilloWriter writer = new(contest, Me, new ContestEntry { SentExchange = "14" });
+
+        string line = writer.QsoLine(Contact() with { Exchange1 = "25" });
+
+        Assert.Equal(
+            "QSO: 14025 CW 2026-05-30 1234 DL1ABC        599  14   JA1XYZ        599  25   ",
+            line);
+    }
+
+    /// A value longer than its column is cut rather than pushing the columns
+    /// after it out of line, which is what N1MM writes.
+    [Fact]
+    public void AValueTooLongForItsColumnIsCut()
+    {
+        UserDefinedContest contest = new(UdcFile.Parse("""
+            [Contest]
+            Name=TIGHT
+            CabrilloString=Exchange1, 3
+            """));
+        CabrilloWriter writer = new(contest, Me);
+
+        Assert.EndsWith("ABC ", writer.QsoLine(Contact() with { Exchange1 = "ABCDEF" }));
+    }
+
+    [Fact]
+    public void TheCabrilloVersionComesFromTheContest()
+    {
+        UserDefinedContest contest = new(UdcFile.Parse("""
+            [Contest]
+            Name=OLD
+            CabrilloVersion=2.0
+            """));
+        CabrilloWriter writer = new(contest, Me);
+
+        Assert.StartsWith(
+            "START-OF-LOG: 2.0",
+            writer.Write(new CabrilloHeader { Contest = "OLD", Callsign = "DL1ABC" }, []));
+    }
 }