basic summaries for all pair classes, create partial classes and condense models into a single file

LightlessSync/PlayerData/Pairs/PairStateCache.cs

@@ -6,6 +6,9 @@ using LightlessSync.Utils;
 
 namespace LightlessSync.PlayerData.Pairs;
 
+/// <summary>
+///     cache for character/pair data and penumbra collections
+/// </summary>
 public sealed class PairStateCache
 {
     private readonly ConcurrentDictionary<string, PairState> _cache = new(StringComparer.Ordinal);