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/DupeScope.cs

@@ -0,0 +1,17 @@
+namespace Nonemm.Contests;
+
+/// When a station may be worked again.
+public enum DupeScope
+{
+    /// Once in the whole contest.
+    Once,
+
+    /// Once per band, whatever the mode.
+    PerBand,
+
+    /// Once per band and mode.
+    PerBandAndMode,
+
+    /// Once per mode, whatever the band.
+    PerMode,
+}