sctp: implement SNAP / sctp-init (#3327)

implements
[draft-hancke-tsvwg-snap.html](https://datatracker.ietf.org/doc/draft-hancke-tsvwg-snap/),
i.e. moving the sctp handshake to out-of-band negotiation as
`a=sctp-init` in the SDP which saves two network round-trips.

(based on #3326, sctp changes in pion/sctp#449)

Add WithRenominationNominationAttribute

Allow a user to set what Attribute value is used

Fix deadlock in ICEGatherer

Patch #3358 introduced a deadlock that is triggered when
ICEGatherer.GracefulShutdown() is called and ICE agent has not closed
its routine yet.

GracefulShutdown() first locks ICEGatherer's mutex, then waits for the
agent routine to close, but the agent routine locks the same mutex too,
resulting in the deadlock.

This patch solves the issue by creating a dedicated mutex for the
candidate pool and using that instead of the main one inside the agent
routine.

Upgrade ICE to fix a NOMINATION bug

Fix nil panic in ICECandidatePair.String()

Upgrade dtls to v3.1.2

Upgrade dtls to fix interop with OpenSSL

Upgrade dtls to fix CVE-2026-26014

Upgrade to dtls options

Update sctp to fix regression