Configure kanta event loggers at import time, inheriting the root level.

configure_logging() now runs with default arguments when kanta.logging
is imported, attaching a plain stderr handler with propagate=False to
the event loggers (kanta.bootstrap/migration/transaction) that carry
Kanta-rendered output.  No levels are set by default, so event output
inherits the effective root level: a framework switching root between
INFO in development and WARNING in production governs Kanta output too.

Other configure_logging changes: channel enable flags use
logger.disabled (propagate toggling no longer silences now that event
loggers have their own handler), skiproot=False removes Kanta's
handler and re-enables propagation so the root logger renders event
output, and debug=True lifts only the DEBUG-emitting loggers
(bootstrap, migration) to DEBUG instead of setting a level on the
"kanta" parent.

tests/conftest.py

@@ -1,3 +1,5 @@
+import logging
+
 import pytest
 
 from kanta.serialization import JsonSerializer, MsgPackSerializer
@@ -12,3 +14,20 @@ from kanta.serialization import JsonSerializer, MsgPackSerializer
 )
 def format_config(request):
     return request.param
+
+
+@pytest.fixture(autouse=True)
+def _kanta_event_loggers_propagate():
+    """Let kanta's event loggers propagate so caplog captures their records.
+
+    Kanta configures them with ``propagate = False`` at import time, which
+    would hide their records from pytest's root-logger capture handler.
+    """
+    names = ("kanta.bootstrap", "kanta.migration", "kanta.transaction")
+    loggers = [logging.getLogger(name) for name in names]
+    previous = [logger.propagate for logger in loggers]
+    for logger in loggers:
+        logger.propagate = True
+    yield
+    for logger, propagate in zip(loggers, previous):
+        logger.propagate = propagate