fix: preserve blank query params in signed URL round-trip

Pass keep_blank_values=True to parse_qsl so empty-valued parameters
(e.g. param=) in the signed URL are not silently dropped.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kraenhansen

src/elevenlabs/conversational_ai/conversation.py

@@ -440,7 +440,7 @@ def _get_signed_url(self):
         signed_url = response.signed_url
         # Append source and version query parameters to the signed URL
         parsed = urllib.parse.urlparse(signed_url)
-        existing_params = urllib.parse.parse_qsl(parsed.query)
+        existing_params = urllib.parse.parse_qsl(parsed.query, keep_blank_values=True)
         existing_params.extend([("source", "python_sdk"), ("version", __version__)])
         return urllib.parse.urlunparse(parsed._replace(query=urllib.parse.urlencode(existing_params)))