Fix frozen delta watermark and add error stats, lazy source, concurrent disk reads, and per-engine config

tests/test_logging.py

@@ -0,0 +1,24 @@
+from loguru import logger
+
+import sqlmem
+
+
+def test_add_sink_idempotent_no_duplicate_lines():
+    """Calling add_sink twice for the same sink must not duplicate log lines."""
+    sqlmem._added_sinks.clear()
+    msgs: list[str] = []
+    sink = lambda message: msgs.append(str(message))  # noqa: E731
+
+    try:
+        sqlmem.add_sink(sink, level="DEBUG", colorize=False)
+        sqlmem.add_sink(sink, level="DEBUG", colorize=False)  # second call: no-op
+        assert len(sqlmem._added_sinks) == 1
+
+        # Emit one record that passes the "sqlmem" name filter.
+        logger.patch(lambda r: r.update(name="sqlmem")).info("hello sqlmem")
+        assert sum("hello sqlmem" in m for m in msgs) == 1
+    finally:
+        for handler_id in sqlmem._added_sinks.values():
+            logger.remove(handler_id)
+        sqlmem._added_sinks.clear()
+        logger.disable("sqlmem")  # restore the default-silent state for other tests