Add the core, contest, storage and format layers

Frequencies, bands, modes, callsigns, grid squares and the country file live in
Nonemm.Core. Nonemm.Contests holds the scoring engine and CQ WW and CQ WPX.
Nonemm.Storage writes N1MM's DXLOG schema, and Nonemm.Formats writes Cabrillo
3.0 and reads and writes ADIF.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Nonemm.Contests/CabrilloExchange.cs

@@ -0,0 +1,11 @@
+namespace Nonemm.Contests;
+
+/// One column of a Cabrillo QSO line. Sponsors read these by column, so each
+/// carries the width it is padded to.
+public sealed record CabrilloField(string Value, int Width);
+
+/// The exchange columns of one Cabrillo QSO line, in the order the sponsor's
+/// template lists them.
+public sealed record CabrilloExchange(
+    IReadOnlyList<CabrilloField> Sent,
+    IReadOnlyList<CabrilloField> Received);