addMiddleware static method
Adds a global middleware to be notified of DI events.
Registration is idempotent by instance identity.
If token is provided, registration is unique per token:
adding another middleware with the same token replaces the previous one.
Implementation
static void addMiddleware(LevitScopeMiddleware middleware, {Object? token}) {
if (token != null) return _addMiddlewareWithToken(token, middleware);
if (_middlewares.contains(middleware)) return;
_middlewares.add(middleware);
}