feat: add AsNativeArray() read‑only accessor to NetworkList<T> (#3567)

Continues: #3562 from @harayuu9

This PR exposes the contents of a `NetworkList<T>` as a **read‑only
`NativeArray<T>`**.
It addresses the recurring need to interoperate efficiently with
Burst‑compiled or `IJob`‑based code without paying the cost of
element‑wise copies or allocations.
The accessor simply forwards `m_List.AsReadOnly()`, preserving
zero‑allocation semantics while respecting `NativeArray`’s lifetime
constraints (call‑site must guarantee the list is not mutated or
disposed).
No behavioural changes are introduced—only a pure additive surface‑area
expansion.

## Changelog

- Added: `NetworkList<T>.AsNativeArray()` to return the list contents as
a `NativeArray<T>.ReadOnly`.

## Testing and Documentation

- No tests have been added.
- Includes documentation for the newly added public API function.

## Backport

This adds a new API surface area and so no backport is required.

---------

Co-authored-by: Yuto Harada <[email protected]>

Author: EmandM

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -10,6 +10,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Added
 
+- Added `AsNativeArray()` read‑only accessor to `NetworkList<T>` (#3567)
 
 ### Fixed
 

com.unity.netcode.gameobjects/Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -631,6 +631,24 @@ public T this[int index]
             }
         }
 
+        /// <summary>
+        /// Gets a **zero‑allocation**, <see cref="NativeArray{T}.ReadOnly"/> view over the current
+        /// elements of this <see cref="NetworkList{T}"/>.
+        /// </summary>
+        /// <remarks>
+        /// The returned array stays valid **only until** the list is mutated (add, remove,
+        /// clear, resize) or <see cref="Dispose()"/> is called on the container.  Continuing to use
+        /// the array after it is invalid will result in undefined behaviour;
+        /// callers are responsible for ensuring a safe lifetime.
+        /// </remarks>
+        /// <returns>
+        /// A <see cref="NativeArray{T}.ReadOnly"/> reference that shares the same backing memory as this list.
+        /// </returns>
+        public NativeArray<T>.ReadOnly AsNativeArray()
+        {
+            return m_List.AsReadOnly();
+        }
+
         private void HandleAddListEvent(NetworkListEvent<T> listEvent)
         {
             m_DirtyEvents.Add(listEvent);