style(trackerobjects): drop internal modifiers and accessor-pair on Bindings

Aligns with the project's STYLE.md preference for plain public fields:

- BasisTrackerBinding's bookkeeping fields (PickupRef, RigidRef,
  PreBindKinematic, HasKinematicCaptured) move from internal to public.
- BasisTrackerObjectManager.Bindings drops the get-only auto-property
  in favour of a public static readonly field — same read-only-ref
  semantics, no property accessor cost, no walling-off ceremony.
- REQUIREMENTS.md spec line updated to match.

Author: towneh

Basis/Packages/com.basis.trackerobjects/REQUIREMENTS.md

@@ -46,7 +46,7 @@ public static class BasisTrackerObjectManager
 {
     public const int RenderPriority = 99;
 
-    public static List<BasisTrackerBinding> Bindings { get; }
+    public static readonly List<BasisTrackerBinding> Bindings;
 
     public static event Action<BasisTrackerBinding> OnBindingCreated;
     public static event Action<BasisTrackerBinding> OnBindingRemoved;

Basis/Packages/com.basis.trackerobjects/Runtime/BasisTrackerBinding.cs

@@ -14,9 +14,9 @@ public class BasisTrackerBinding
         public Vector3 LocalPositionOffset;
         public Quaternion LocalRotationOffset;
 
-        internal BasisPickupInteractable PickupRef;
-        internal Rigidbody RigidRef;
-        internal bool PreBindKinematic;
-        internal bool HasKinematicCaptured;
+        public BasisPickupInteractable PickupRef;
+        public Rigidbody RigidRef;
+        public bool PreBindKinematic;
+        public bool HasKinematicCaptured;
     }
 }

Basis/Packages/com.basis.trackerobjects/Runtime/BasisTrackerObjectManager.cs

@@ -11,7 +11,7 @@ public static class BasisTrackerObjectManager
     {
         public const int RenderPriority = 99;
 
-        public static List<BasisTrackerBinding> Bindings { get; } = new List<BasisTrackerBinding>();
+        public static readonly List<BasisTrackerBinding> Bindings = new List<BasisTrackerBinding>();
 
         public static event Action<BasisTrackerBinding> OnBindingCreated;
         public static event Action<BasisTrackerBinding> OnBindingRemoved;