sdp: keep end-of-candidates when parsing an SDP fragment

[RaphaelFakhri]

SDPFragment.Unmarshal drops the a=end-of-candidates attribute, so a trickle ICE fragment that signals the end of candidates never reaches Marshal or PatchICECredentialAndCandidatesIntoSDP.

The parser handles attributes without a value (no :) in an early branch that only recognizes ice-lite and then continues. The case sdp.AttrKeyEndOfCandidates in the switch below that branch is unreachable, because end-of-candidates never contains a colon.

This change handles end-of-candidates in the no-value branch and removes the dead case. The fragment's Marshal output and the SDP produced by PatchICECredentialAndCandidatesIntoSDP now carry the attribute, as the code intends.

Testing

TestSDPFragmentEndOfCandidates parses a fragment that ends with a=end-of-candidates, checks that Marshal round-trips it, and checks that patching the fragment into an offer adds the attribute to the media section. On current main the test fails because the marshalled output lacks the attribute. With the change, go test -race ./sdp passes.

A changeset is included.

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Latest commit: 1351bbc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
github.com/livekit/protocol	Patch
@livekit/protocol	Patch

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