Add an overridable socket_factory to dns.quic (like dns.query has)

[tykling]

Motivation
dns.query allows me to override the socket creation function for tcp, udp, doh by overriding socket_factory here:

dnspython/dns/query.py

Line 177 in a977e61

socket_factory = socket.socket

This works great!

But the quic code uses socket.socket directly:

dnspython/dns/quic/_sync.py

Line 78 in a977e61

self._socket = socket.socket(self._af, socket.SOCK_DGRAM, 0)

Locally I am using a tiny 2 line patch to quic/sync.py which just changes the direct use of socket.socket to be use of socket_factory instead, just like in dns.query. I can then override socket_factory in my own code for proxyfication.

Describe the solution you'd like.
I would like to be able to override the socket used to easily use a proxy server with dnspython. The solution above works great for sync but something else/more is needed for the async cases. I haven't played around with async at all while testing this.

I can open a PR with the patch for _sync.py but I wanted to gauge the interest first.

Thanks!

[rthalley]

I'd be ok with adding a socket_factory to quic/_sync.py; I think it has to be there (rather than reusing query's socket_factory) for circularity reasons. I don't think you have to worry about async as it already abstracts socket creation with the make_socket() backend method, so if someone needed to change it they could subclass the backend.

[tykling]

Great! I've opened a small PR let me know if you need anything else, and thank you for the fast response :)

[rthalley]

Merged, thanks!