Uphold server constraints

[julian-graf]

• Primarily introduces checks to not cause protocol errors on the following options:
  • prevent SUBSCRIBE packets with shared subscription topic filters when shared subscription available = 0
  • prevent SUBSCRIBE packets with wildcard subscription topic filters when wildcard subscription available = 0
  • prevent SUBSCRIBE packets with subscription identifier when subscription identifiers available = 0
  • prevent PUBLISH packets with QoS > server maximum QoS
  • prevent PUBLISH packets with retain flag set when retain available = 0
• Introduces NonZero<u16> for topic aliases as topic aliases are not allowed to be 0
• Replace MqttError::InvalidTopicAlias with the new MqttError::UnsupportedByServer variant
• Move ConnectInfo into crate::client::event and rename to Connected, delete the crate::client::info module
• Update & improve documentation