Go 1.19 DNS improvments

[ThinkChaos]

I read through Go 1.19's changelog draft and they mention a couple DNS improvements I thought could interest people here:

The pure Go resolver will now use EDNS(0) to include a suggested maximum reply packet length, permitting reply packets to contain up to 1232 bytes (the previous maximum was 512). In the unlikely event that this causes problems with a local DNS resolver, setting the environment variable GODEBUG=netdns=cgo to use the cgo-based resolver should work. Please report any such problems on the issue tracker.

When a net package function or method returns an "I/O timeout" error, the error will now satisfy errors.Is(err, context.DeadlineExceeded). When a net package function returns an "operation was canceled" error, the error will now satisfy errors.Is(err, context.Canceled). These changes are intended to make it easier for code to test for cases in which a context cancellation or timeout causes a net package function or method to return an error, while preserving backward compatibility for error messages.

Resolver.PreferGo is now implemented on Windows and Plan 9. It previously only worked on Unix platforms. Combined with Dialer.Resolver and Resolver.Dial, it's now possible to write portable programs and be in control of all DNS name lookups when dialing.

The net package now has initial support for the netgo build tag on Windows. When used, the package uses the Go DNS client (as used by Resolver.PreferGo) instead of asking Windows for DNS results. The upstream DNS server it discovers from Windows may not yet be correct with complex system network configurations, however.

Maybe we could also enable EDNS(0) by default for any requests initiated by blocky (bootstrap and lists basically)?

And good news (though not sure how many people use Windows, or Plan 9), the limitation of bootstrap not working on Windows will be lifted.