Unbundle the `decorator` dependency, or at least upgrade it

Hi,

In #91 years ago, it was decided to add the decorator to fix a problem. Back then choices was made to not add a new dependency, but really bundle the only decorar file needed. Distributions (in my case Fedora) usually prefer to rely on the actual package than bundled dependencies. Fedora does apply a patch to unbundle decorator, maybe other distro do that too.

Do we still want to avoid dependencies in 2025 ? I have seen other discussions where it was discussed adding a protobuf dependency, which pulls many more dependencies, so isn't ok now to depend on decorator ?

If not, would it make sense at least to upgrade it ? By doing so, you hit the issue that decorator.getargspec has been removed years ago. In python 3 there is now inspect.getfullargspec which is not strictly equivalent but does provide a similar feature. Fedora uses a minimal patch here: https://src.fedoraproject.org/rpms/python-prometheus_client/blob/rawhide/f/0001-Remove-the-bundled-decorator-package.patch#_506 but tries to avoid adding much code, most likely the "real" change is more verbose.

En la issue no se menciona ningún archivo del repositorio ni ninguna prueba. Empieza revisando la implementación actual del decorador incluida en el paquete y el parche de unbundling de Fedora enlazado; después, determina si el proyecto dependerá del paquete externo o conservará una versión incluida en el paquete y actualizada. Se considera terminado cuando la estrategia de dependencias elegida funciona con las versiones actuales de Python y su compatibilidad está cubierta por la suite de pruebas existente.