Adding a boost::hash specialization for IOAddress
With a boost::hash we can use hashed index over IOAddresses (hashed indexes are fasters than ordered when existence is the only wanted property, i.e. when the order never matters).
I propose to simply use the toBytes() when both IPv4 and IPv6 addresses are used and perhaps toUint32() in the rare case the index is only for IPv4 addresses so it is in fact pretty trivial.
https://www.boost.org/doc/libs/1_73_0/doc/html/hash/custom.html for the reference