v2.6.0

• dht: added early announce/listen mechanism, significantly reducing the time taken for the first values to be published or received for a new search, without major trade-off.
• dht: fixed an issue that was causing invalid transaction IDs to be occasionally used
• dht: changed user agent to "o2"
• dhtinterface: added setOnPublicAddressChanged to listen for public address changes
• dhtrunner: added Context::publicAddressChangedCb to make use of the new API
• log: new logger API using {fmt}
• http: added static method Request::url_encode to encode url parameters.
• docker: Alpine image now based on Alpine 3.18
• build/meson: build dhtchat, dhtscanner