fix: Change IterableAsyncQueue to public access modifier (#122)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> **Low Risk**
> Single visibility change with no functional logic changes; main risk
is expanding the supported public API surface.
> 
> **Overview**
> Makes `IterableAsyncQueue` in `lib/shared/common` publicly accessible
by changing the class access modifier from package-private to `public`,
enabling reuse by other packages/modules without code changes to its
behavior.
> 
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Author: kinyoklion

lib/shared/common/src/main/java/com/launchdarkly/sdk/collections/IterableAsyncQueue.java

@@ -17,7 +17,7 @@
  *
  * @param <T> the type of elements held in this queue
  */
-class IterableAsyncQueue<T> {
+public class IterableAsyncQueue<T> {
     private final Object lock = new Object();
     private final LinkedList<T> queue = new LinkedList<>();