Non-string param value breaks MLflow client get_run and others

[suprjinx]

if a param.value is an int or float and returned as such, the Mlflow client will ghack:
6: E google.protobuf.json_format.ParseError: Failed to parse run field: Failed to parse data field: Failed to parse params field: Failed to parse value field: expected string or bytes-like object, got 'float'....