we want to be able to have multiple locally bound dns sockets in lokinet so
i restructured most of the dns subsystem in order to make this easier.
specifically, we have a new structure to dns subsystem:
* dns::QueryJob_Base
base type for holding a dns query and response with virtual methods
in charge of sending a reply to whoever requested.
* dns::PacketSource_Base
base type for reading and writing dns messages to and from wherever they came from
* dns::Resolver_Base
base type for filtering and handling of dns messages asynchronously.
* dns::Server
contextualized per endpoint dns object, responsible for all dns related isms.
this change hides all impelementation details of all of the dns components.
adds some more helper functions for parsing dns and dealing with OwnedBuffer.
overall dns becomes less of a pain with this new structure. probably.
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