Upgrade TURN to v6, STUN to v5, and DTLS to v4

Stabilize ICE-lite priorities like libwebrtc

History:
PR #959 let ICE-lite agents pick the best pair locally without sending
checks. All lite host candidates had the same priority, so with
several candidates the two sides could pick different pairs and fail
to connect. #968 fixed that by stepping each new lite candidate down
from the default until its priority was unique. That made priorities
depend on gather order: the same address could get a different
priority on another node, or depending on whether the node was
single- or dual-stack.

The main problem is that Pion doesn't have local preference like
libwebrtc, instead of doing other hacks this adds:
`(counter << 8) | address precedence`. The low byte is the RFC 6724
precedence of the address (IPv6 40, IPv4 30, and so on), so address
families never collide. The counter drops only to separate candidates
of the same family. A candidate's priority no longer depends on gather
order or on whether the agent is single- or dual-stack.

Unlike libwebrtc, the high byte is not a network adapter preference,
since Pion has no adapter types.

Stabilize ICE-lite priorities like libwebrtc

History:
PR #959 let ICE-lite agents pick the best pair locally without sending
checks. All lite host candidates had the same priority, so with
several candidates the two sides could pick different pairs and fail
to connect. #968 fixed that by stepping each new lite candidate down
from the default until its priority was unique. That made priorities
depend on gather order: the same address could get a different
priority on another node, or depending on whether the node was
single- or dual-stack.

The main problem is that Pion doesn't have local preference like
libwebrtc, instead of doing other hacks this adds:
`(counter << 8) | address precedence`. The low byte is the RFC 6724
precedence of the address (IPv6 40, IPv4 30, and so on), so address
families never collide. The counter drops only to separate candidates
of the same family. A candidate's priority no longer depends on gather
order or on whether the agent is single- or dual-stack.

Unlike libwebrtc, the high byte is not a network adapter preference,
since Pion has no adapter types.

Send prflx type preference in PRIORITY attribute on v4 (#1045)

cherry pick #1026

Co-authored-by: Ilay David <ilay@decart.ai>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Preserve pre-created mux connections on restart

Skip mux ufrag cleanup during the initial Restart call in NewAgent
preserves connections created by listeners before constructing.

Found this while working on SCTP automated benchmarks.

Use 64 bit candidate pair packet counters

packetsSent and packetsReceived are unsigned long long in the
specification since w3c/webrtc-stats#494

Request relayed address in the candidate family

When only a single candidate family is configured, request the relayed
address in that family, even if the TURN server is reached over the
other family. Previously, the TURN server allocated the relay in the
transport's family, and ice then discarded it.

sped: keep the DTLS 1.3 server's packets on handshake completion (#1024)

The DTLS 1.3 server completes when it receives the client's Finished but
still has to ACK it. That ACK may be queued before completion is
signaled and dropping the outgoing packets loses it, so the client
retransmits its last flight a second later.

Only the DTLS 1.2 client has nothing more to send and drops its packets,
while it keeps sending ACK attributes until it receives the server's
last flight.

(comment now matches what I wrote in libwebrtc)

Update mdns to fix compatibility with Chromium

Update mdns to fix compatibility with Chromium