Fix race condition in initialization - eagerly load properties

- Eagerly load SuperProperties, OnceProperties, and TimedEvents during Initialize()
- Pre-cache auto properties (events and engage) before first Track() call
- Initialize session metadata during Initialize() to ensure it's ready
- Prevents race condition where Track() called before properties loaded from disk

This fixes the issue where App Start events were missing super properties
when Track() was called immediately after Init().

Addresses customer report of 30-44% event volume drop and missing super
properties on first event after migrating to Unity SDK v3.5.3.

Co-authored-by: jaredmixpanel <10504508+jaredmixpanel@users.noreply.github.com>

Author: Copilot

Mixpanel/Controller.cs

@@ -49,6 +49,19 @@ internal static void Initialize() {
             // Copy over any runtime changes that happened before initialization from settings instance to the config.
             MixpanelSettings.Instance.ApplyToConfig();
             GetInstance();
+            
+            // Eagerly load all persisted properties to ensure they're available immediately for tracking
+            // This prevents race conditions where Track() is called before properties are loaded from disk
+            var _ = MixpanelStorage.SuperProperties;
+            var __ = MixpanelStorage.OnceProperties;
+            var ___ = MixpanelStorage.TimedEvents;
+            
+            // Pre-cache auto properties so they're ready for the first Track() call
+            GetEventsDefaultProperties();
+            GetEngageDefaultProperties();
+            
+            // Initialize session metadata
+            Metadata.InitSession();
         }
 
         internal static bool IsInitialized() {