JSON backing store, I/O fixes, Networking Security

Introduced Newtonsoft.Json-backed persistence.
Improved backing-store reliability and serialization across the caching stack.
Improved networking security posture.

Key changes:
- Add new GameCult.Caching.NewtonsoftJson project with SingleFile/MultiFile backing stores and polymorphic known-type envelopes.
- Add MessagePack helper serialization (DatabaseEntrySerialization) and update MessagePack backing stores to use the shared options/resolver; add DatabaseLink formatter and generator/analyzer docs.
- Update CultLib.sln to include the new projects and new caching tests project.
- Improve CultCache persistence behavior: track pending store operations, wait for operations on PullAll, and centralize async push handling with error logging.
- Harden file I/O in multi-file/single-file stores: atomic temp-file writes, safe Replace/Move semantics, rename-safe deletes, and improved file-watcher subscription and debounce disposal.
- Add README files and documentation for several subprojects and packaging projects.

These changes add JSON persistence support, improve serialization consistency, and make on-disk operations more robust and observable.

src/GameCult.Logging.Unity/UnityLogger.cs

@@ -3,29 +3,36 @@ using UnityEngine;
 
 namespace GameCult.Logging.Unity
 {
+    /// <summary>
+    /// Adapts <see cref="ILogger"/> calls to Unity's logging facilities.
+    /// </summary>
     public class UnityLogger : ILogger
     {
         private readonly bool _isDebugBuild = Debug.isDebugBuild;  // Cache Unity-specific
 
+        /// <inheritdoc />
         public void LogInfo(string message)
         {
             Observable.NextFrame().Subscribe(_ => Debug.Log($"[INFO] {message}"));
         }
 
+        /// <inheritdoc />
         public void LogWarning(string message)
         {
             Observable.NextFrame().Subscribe(_ => Debug.LogWarning($"[WARN] {message}"));
         }
 
+        /// <inheritdoc />
         public void LogError(string message)
         {
             Observable.NextFrame().Subscribe(_ => Debug.LogError($"[ERROR] {message}"));
         }
 
+        /// <inheritdoc />
         public void LogDebug(string message)
         {
             if (_isDebugBuild)
                 Observable.NextFrame().Subscribe(_ => Debug.Log($"[DEBUG] {message}"));
         }
     }
-}
+}