Fix: Enhance logging for OSError and prevent AttributeError

This commit addresses two potential issues related to issue #50:

1.  Enhanced `OSError` Logging in `utils.py`:
    The `printResponse` function in `src-python/utils.py` has been modified
    to include more robust error handling around the `json.dumps()` call.
    If an `OSError` (such as `[Errno 22] Invalid argument`) occurs during
    JSON serialization, the function will now:
    - Log the full traceback of the OSError.
    - Log the specific problematic response dictionary that caused the error.
    - Print a fallback JSON error message to stdout.
    This change aims to help diagnose the root cause of the `OSError`
    reported by you by capturing the exact data that triggers it.

2.  Prevent `AttributeError` for `.close()` calls:
    Added checks in `src-python/models/osc/osc.py` and
    `src-python/models/websocket/websocket_server.py` to ensure that
    objects are not `None` before their `.close()` or `.cancel()` methods
    are called. This specifically addresses:
    - `self.browser.zc.close()` and `self.browser.browser.cancel()` in `osc.py`.
    - `self._loop.close()` in `websocket_server.py`.
    These changes prevent potential `AttributeError: 'NoneType' object
    has no attribute 'close'` errors if these objects are not fully
    initialized before cleanup.

src-python/models/osc/osc.py

@@ -90,8 +90,10 @@ class OSCHandler:
             # エラー発生時にbrowserをリセットして次回再初期化
             if self.browser is not None:
                 try:
-                    self.browser.zc.close()
-                    self.browser.browser.cancel()
+                    if hasattr(self.browser, 'zc') and self.browser.zc is not None:
+                        self.browser.zc.close()
+                    if hasattr(self.browser, 'browser') and self.browser.browser is not None:
+                        self.browser.browser.cancel()
                 except Exception:
                     pass
                 self.browser = None
@@ -140,8 +142,10 @@ class OSCHandler:
         # browserがある場合はクリーンアップ
         if self.browser is not None:
             try:
-                self.browser.zc.close()
-                self.browser.browser.cancel()
+                if hasattr(self.browser, 'zc') and self.browser.zc is not None:
+                    self.browser.zc.close()
+                if hasattr(self.browser, 'browser') and self.browser.browser is not None:
+                    self.browser.browser.cancel()
             except Exception:
                 pass
             self.browser = None

src-python/models/websocket/websocket_server.py

@@ -138,7 +138,8 @@ class WebSocketServer:
         finally:
             # 停止指示が出たらすべての接続を閉じ、イベントループを終了
             self._loop.run_until_complete(self._shutdown())
-            self._loop.close()
+            if self._loop is not None:
+                self._loop.close()
 
     async def _shutdown(self):
         """