add coroutine priority support to TrueAsync API

  Implements priority-based coroutine scheduling where higher priority values
  result in coroutines being queued at the front of the execution queue.

  ## Changes

  ### Circular Buffer Enhancement
  - Add `circular_buffer_push_front()` function to insert elements at buffer head
  - Fallback to normal push when front insertion is not possible (buffer full)

  ### API Extension
  - Update `zend_async_spawn_t` typedef to include `int32_t priority` parameter
  - Add new macros:
    - `ZEND_ASYNC_SPAWN_WITH_PRIORITY(priority)`
    - `ZEND_ASYNC_SPAWN_WITH_SCOPE_EX(scope, priority)`
  - Maintain backward compatibility by updating existing macros to pass priority=0

  ### Priority Logic
  - Priority > 0: coroutine queued at front (high priority)
  - Priority ≤ 0: coroutine queued at back (normal/low priority)
  - Preserves existing behavior for all current code

  ### Files Modified
  - `ext/async/internal/circular_buffer.{h,c}` - Buffer front insertion
  - `Zend/zend_async_API.{h,c}` - API definitions and stub functions
  - `ext/async/async_API.c` - Priority-aware spawn implementation

  ## Backward Compatibility
  All existing spawn macros unchanged in behavior, new priority parameter
  defaults to 0 for normal scheduling order.

Author: EdmondDantes

Zend/zend_async_API.c

@@ -29,7 +29,7 @@ zend_async_globals_t zend_async_globals_api = {0};
 /* Forward declarations */
 static void zend_async_main_handlers_shutdown(void);
 
-static zend_coroutine_t * spawn(zend_async_scope_t *scope, zend_object *scope_provider)
+static zend_coroutine_t * spawn(zend_async_scope_t *scope, zend_object *scope_provider, int32_t priority)
 {
 	ASYNC_THROW_ERROR("Async API is not enabled");
 	return NULL;

Zend/zend_async_API.h

@@ -184,7 +184,7 @@ typedef struct _zend_async_task_s zend_async_task_t;
 
 typedef zend_coroutine_t * (*zend_async_new_coroutine_t)(zend_async_scope_t *scope);
 typedef zend_async_scope_t * (*zend_async_new_scope_t)(zend_async_scope_t * parent_scope, bool with_zend_object);
-typedef zend_coroutine_t * (*zend_async_spawn_t)(zend_async_scope_t *scope, zend_object *scope_provider);
+typedef zend_coroutine_t * (*zend_async_spawn_t)(zend_async_scope_t *scope, zend_object *scope_provider, int32_t priority);
 typedef void (*zend_async_suspend_t)(bool from_main);
 typedef void (*zend_async_enqueue_coroutine_t)(zend_coroutine_t *coroutine);
 typedef void (*zend_async_resume_t)(zend_coroutine_t *coroutine, zend_object * error, const bool transfer_error);
@@ -1231,9 +1231,11 @@ ZEND_API void zend_async_call_main_coroutine_start_handlers(zend_coroutine_t *ma
 END_EXTERN_C()
 
 #define ZEND_ASYNC_IS_ENABLED() zend_async_is_enabled()
-#define ZEND_ASYNC_SPAWN() zend_async_spawn_fn(NULL, NULL)
-#define ZEND_ASYNC_SPAWN_WITH(scope) zend_async_spawn_fn(scope, NULL)
-#define ZEND_ASYNC_SPAWN_WITH_PROVIDER(scope_provider) zend_async_spawn_fn(NULL, scope_provider)
+#define ZEND_ASYNC_SPAWN() zend_async_spawn_fn(NULL, NULL, 0)
+#define ZEND_ASYNC_SPAWN_WITH(scope) zend_async_spawn_fn(scope, NULL, 0)
+#define ZEND_ASYNC_SPAWN_WITH_PROVIDER(scope_provider) zend_async_spawn_fn(NULL, scope_provider, 0)
+#define ZEND_ASYNC_SPAWN_WITH_PRIORITY(priority) zend_async_spawn_fn(NULL, NULL, priority)
+#define ZEND_ASYNC_SPAWN_WITH_SCOPE_EX(scope, priority) zend_async_spawn_fn(scope, NULL, priority)
 #define ZEND_ASYNC_NEW_COROUTINE(scope) zend_async_new_coroutine_fn(scope)
 #define ZEND_ASYNC_NEW_SCOPE(parent) zend_async_new_scope_fn(parent, false)
 #define ZEND_ASYNC_NEW_SCOPE_WITH_OBJECT(parent) zend_async_new_scope_fn(parent, true)