Delegate fiber GC to coroutine when fiber has coroutine

When fiber->coroutine is set, the fiber's GC handler now delegates
to the coroutine's GC handler by adding the coroutine object to GC buffer.
This ensures proper garbage collection of coroutine data including:
- fcall parameters and function name
- coroutine result
- execution stack
- all other coroutine-managed resources

For non-coroutine fibers, the original GC logic remains unchanged.

Author: Edmond

Zend/zend_fibers.c

@@ -1375,18 +1375,26 @@ static HashTable *zend_fiber_object_gc(zend_object *object, zval **table, int *n
 	zend_get_gc_buffer *buf = zend_get_gc_buffer_create();
 
 	/*
-	 * For coroutine path add fcall to GC (if ownership not taken).
-	 * For non-coroutine path add fci and result to GC.
+	 * For coroutine path: add coroutine object to GC.
+	 * GC will call coroutine's get_gc handler which handles fcall, result, and execution stack.
 	 */
-	if (fiber->coroutine != NULL && fiber->fcall != NULL) {
-		zend_get_gc_buffer_add_zval(buf, &fiber->fcall->fci.function_name);
-		zend_get_gc_buffer_add_zval(buf, &fiber->coroutine->result);
-		/* result in coroutine->result - coroutine's GC handles it */
-	} else {
-		zend_get_gc_buffer_add_zval(buf, &fiber->fci.function_name);
-		zend_get_gc_buffer_add_zval(buf, &fiber->result);
+	if (fiber->coroutine != NULL) {
+		zend_object *coroutine_obj = ZEND_ASYNC_EVENT_TO_OBJECT(&fiber->coroutine->event);
+		zend_get_gc_buffer_add_obj(buf, coroutine_obj);
+
+		/* Add fcall if it's still owned by fiber (not yet transferred to coroutine) */
+		if (fiber->fcall != NULL) {
+			zend_get_gc_buffer_add_zval(buf, &fiber->fcall->fci.function_name);
+		}
+
+		zend_get_gc_buffer_use(buf, table, num);
+		return NULL;
 	}
 
+	/* Non-coroutine path: add fci and result to GC */
+	zend_get_gc_buffer_add_zval(buf, &fiber->fci.function_name);
+	zend_get_gc_buffer_add_zval(buf, &fiber->result);
+
 	if (fiber->context.status != ZEND_FIBER_STATUS_SUSPENDED || fiber->caller != NULL) {
 		zend_get_gc_buffer_use(buf, table, num);
 		return NULL;