Reload the pyo3-log config when the Python logging config changes. (#14976)

Since pyo3-log is initialized very early in the Python start-up
it caches the state of the loggers before they're fully initialized
(and thus are essentially disabled). Whenever we reload the
logging configuration we now also tell pyo3-log to discard
any cached logging configuration it has; it will refetch the
current logging configuration from Python at the next point
it logs.

This fixes Rust log lines not appearing in the homeserver logs.