fix/fuzz: Implement `quicly_num_streams_by_group`
fix/fuzz: Implement `quicly_num_streams_by_group`

devnexen/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o,h2o/h2o,h2o/h2o,h2o/h2o,yannick/h2o,yannick/h2o,h2o/h2o,yannick/h2o,yannick/h2o,yannick/h2o,h2o/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,devnexen/h2o