perf(core): Skip Hint allocation in addBreadcrumb without callback (JAVA-605)

Only allocate a Hint when a beforeBreadcrumb callback is set. addBreadcrumb
previously allocated a Hint (HashMap + ArrayList + lock) on every call even
though the Hint is only ever passed to the callback, wasting allocations on
the common no-callback path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: runningcode

sentry/src/main/java/io/sentry/Scope.java

@@ -493,12 +493,11 @@ public void addBreadcrumb(@NotNull Breadcrumb breadcrumb, @Nullable Hint hint) {
     if (breadcrumb == null || breadcrumbs instanceof DisabledQueue) {
       return;
     }
-    if (hint == null) {
-      hint = new Hint();
-    }
-
     SentryOptions.BeforeBreadcrumbCallback callback = options.getBeforeBreadcrumb();
     if (callback != null) {
+      if (hint == null) {
+        hint = new Hint();
+      }
       breadcrumb = executeBeforeBreadcrumb(callback, breadcrumb, hint);
     }
     if (breadcrumb != null) {