The documentation for Environment's BoundClass methods (process(),
timeout(), event(), etc.) is moved from simpy.core.rst to core.py. The
docstrings are now associated with the TYPE_CHECKING-only stubs and Sphinx
now documents using those stubs.

Other classes with BoundClass methods are now also documented using the
type checking stubs. The generated API docs thus now show a proper method
signature instead of treating the BoundClass methods as data attributes of
the class.