fix: parse rid and ssrc to proper types

This caused a TypeError on Safari where rid was "0" and being parsed as
an integer instead of a string.

Author: Yash-Garg

lib/src/rtc_rtp_parameters_impl.dart

@@ -81,7 +81,9 @@ class RTCRtpEncodingWeb {
       'scaleResolutionDownBy': object
           .getProperty<JSNumber?>('scaleResolutionDownBy'.toJS)
           ?.toDartDouble,
-      'ssrc': object.getProperty<JSString?>('ssrc'.toJS)?.toDart
+      'ssrc': int.tryParse(
+        object.getProperty<JSString?>('ssrc'.toJS)?.toDart ?? '0',
+      )
     });
   }
 }