mDNS queries sent via unicast connection instead of multicast - causes discovery failures for certain devices

### Problem
The [`sendQuery` function](https://github.com/hashicorp/mdns/blob/main/client.go#L402) (lines 402-420) sends mDNS queries using **unicast** connections instead of multicast connections.

### Impact
Some devices, e.g. the Alfen EV Charger only responds to queries sent via multicast

### RFC Compliance
According to RFC 6762 (Multicast DNS), service discovery queries should be sent to the multicast address (224.0.0.251 for IPv4, ff02::fb for IPv6). While the library correctly sends to ipv4Addr (which is the multicast address), it uses a unicast socket to do so, which some devices may filter or ignore.

### Question
Should mDNS queries be sent via the multicast connections ipv4MulticastConn/ipv6MulticastConn instead of unicast connections for better compatibility? Or is there a fork that already does this?

Start in client.go at sendQuery (lines 402-420), then trace how ipv4MulticastConn, ipv6MulticastConn, and the unicast connections are initialized and used. Confirm the RFC and device-compatibility implications, with completion defined as selecting the appropriate query transport and verifying discovery behavior for IPv4 and IPv6.

Written by the indexing model from the issue text.