Fix public events API

[deathaxe]

Python 3.13 plugin_host of ST4201+ does no longer support ZipLoader in favor of PEP451 compliant approach.

This commit therefore refactors public package_control module to use only built-in import mechanisms, if possible and fallback to ZipLoader only, if a python 3.3 plugin needs to load events module from Package Control.sublime-package running on foreign python 3.8 or 3.13 host.

With this change behavior is equal on all plugin_hosts. Only events module is exported as this is the only module intended to be public.