Replace log dict toggles with logdiff kwarg and kanta.transaction.diff logger

Per-transaction logdiff=False skips building and printing the diff body,
logging only the header. Globally, configure_logging(diff=False) disables
the kanta.transaction.diff child logger, which now carries all diff lines,
so applications can route or silence diffs separately from headers.

tests/test_logging.py

@@ -30,10 +30,17 @@ def test_colorize_header_parts_missing_user_and_extra():
 @pytest.fixture(autouse=True)
 def _reset_kanta_loggers():
     yield
-    for name in ("kanta", "kanta.transaction", "kanta.bootstrap", "kanta.migration"):
+    for name in (
+        "kanta",
+        "kanta.transaction",
+        "kanta.transaction.diff",
+        "kanta.bootstrap",
+        "kanta.migration",
+    ):
         logger = logging.getLogger(name)
         logger.setLevel(logging.NOTSET)
         logger.propagate = True
+        logger.disabled = False
         logger.handlers.clear()
 
 
@@ -80,30 +87,36 @@ def test_log_change_appends_extra_string(capsys):
     assert f"{_TARGET}mydb.db{_RESET}" in captured.err
 
 
-def test_log_change_log_diff_false(capsys):
+def test_log_change_log_diff_false(capsys, monkeypatch):
     kanta_logger = logging.getLogger("kanta")
     kanta_logger.handlers.clear()
     configure_logging()
+
+    def _boom(*args, **kwargs):
+        raise AssertionError("format_diff should not be called")
+
+    monkeypatch.setattr("kanta.logging.format_diff", _boom)
     log_change("update", {"counter": 5}, previous={}, log_diff=False)
     captured = capsys.readouterr()
     assert "update" in captured.err
     assert "counter" not in captured.err
 
 
-def test_log_change_log_header_false(capsys):
+def test_configure_logging_diff_false(capsys):
     kanta_logger = logging.getLogger("kanta")
     kanta_logger.handlers.clear()
-    configure_logging()
-    log_change("update", {"counter": 5}, previous={}, log_header=False)
+    configure_logging(diff=False)
+    log_change("update", {"counter": 5}, previous={})
+    captured = capsys.readouterr()
+    assert "update" in captured.err
+    assert "counter" not in captured.err
+
+
+def test_configure_logging_diff_true_reenables(capsys):
+    kanta_logger = logging.getLogger("kanta")
+    kanta_logger.handlers.clear()
+    configure_logging(diff=False)
+    configure_logging(diff=True)
+    log_change("update", {"counter": 5}, previous={})
     captured = capsys.readouterr()
-    assert "update" not in captured.err
     assert "counter" in captured.err
-
-
-def test_log_change_both_disabled_logs_nothing(capsys):
-    kanta_logger = logging.getLogger("kanta")
-    kanta_logger.handlers.clear()
-    configure_logging()
-    log_change("update", {"counter": 5}, previous={}, log_header=False, log_diff=False)
-    captured = capsys.readouterr()
-    assert captured.err == ""