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.Core/Country/CountryLookup.cs

@@ -0,0 +1,12 @@
+namespace Nonemm.Core.Country;
+
+/// What the country file says about one callsign. Zone and continent can differ
+/// from the entity's own when the country file overrides them for that prefix.
+public sealed record CountryLookup(
+    DxccEntity Entity,
+    string MatchedPrefix,
+    int CqZone,
+    int ItuZone,
+    string Continent,
+    double Latitude,
+    double Longitude);