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.

tests/test_utils/logging_setup.py

@@ -17,6 +17,7 @@ import os
 import twisted.logger
 
 from synapse.logging.context import LoggingContextFilter
+from synapse.synapse_rust import reset_logging_config
 
 
 class ToTwistedHandler(logging.Handler):
@@ -52,3 +53,5 @@ def setup_logging():
 
     log_level = os.environ.get("SYNAPSE_TEST_LOG_LEVEL", "ERROR")
     root_logger.setLevel(log_level)
+
+    reset_logging_config()