feat(jobs): optimize job data copy and add default opts

Replaces Unsafe.Copy/NativeMemory.Copy with direct pointer assignment for job data in JobScheduler, improving performance and code clarity. Adds a static Default property to AllocationManagerInitOpts for easier initialization. Updates test setup to use the new default options. Bumps assembly version to 1.5.7.

Misaki.HighPerformance.LowLevel/Buffer/AllocationManager.cs

@@ -54,6 +54,13 @@ public readonly struct AllocationManagerInitOpts
     {
         get; init;
     }
+
+    public static AllocationManagerInitOpts Default => new AllocationManagerInitOpts
+    {
+        ArenaCapacity = 1024 * 1024 * 1024, // 1 GB
+        StackCapacity = 16 * 1024 * 1024, // 16 MB per thread
+        FreeListConcurrencyLevel = Environment.ProcessorCount
+    };
 }
 
 /// <summary>