Add __slots__ to EventDispatch.

This class is meant to be inherited,
the subclass should be allowed to use `__slots__`.

Author: HexDecimal

CHANGELOG.md

@@ -4,6 +4,8 @@ Changes relevant to the users of python-tcod are documented here.
 This project adheres to [Semantic Versioning](https://semver.org/) since version `2.0.0`.
 
 ## [Unreleased]
+### Changed
+- Added an empty `__slots__` to `EventDispatch`.
 
 ## [16.1.0] - 2023-06-23
 ### Added

tcod/event.py

@@ -1365,6 +1365,8 @@ def cmd_quit(self) -> None:
                 state.dispatch(event)
     '''
 
+    __slots__ = ()
+
     def dispatch(self, event: Any) -> T | None:
         """Send an event to an `ev_*` method.