Add __repr__ to DqliteConnection

Debugging sessions and logs now show address/database/state instead
of the default <...Connection object at 0x...>.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqliteclient/connection.py

@@ -108,6 +108,12 @@ def is_connected(self) -> bool:
         """Check if connected."""
         return self._protocol is not None
 
+    def __repr__(self) -> str:
+        state = "connected" if self._protocol is not None else "disconnected"
+        return (
+            f"<DqliteConnection address={self._address!r} database={self._database!r} {state}>"
+        )
+
     @property
     def in_transaction(self) -> bool:
         """Check if a transaction is active."""