Publish DTMF Helper for Local Participant

[ayukumar261]

Problem

The JavaScript, Rust, Python, and Node SDKs have DTMF publishing helpers that always use the reliable data channel. The Go SDK has no equivalent, so developers have to build the packet themselves and remember to pass WithDataPublishReliable(true).

That matters because PublishDataPacket has defaulted to the lossy channel since #421 (v2.1.0), and the lossy channel has been unordered since #659 (v2.8.0). Digits sent with the default can be dropped or arrive out of order.

Changes

• Added PublishDTMF(code, digit) to LocalParticipant. It wraps PublishDataPacket with WithDataPublishReliable(true), so a SipDTMF packet always goes over the reliable channel. The helper accepts no publishing options.
• Updated a stale comment above the default in PublishDataPacket. It said the Go default matches the protobuf default. That was true when Accept and send DTMF via data channel #415 wrote it, since both defaulted to reliable. Revert default behavior change with data publishing #421 flipped the Go default to lossy but left the comment, and the protobuf zero value is still RELIABLE.

Testing

TestPublishDTMF publishes 1 2 3 # and asserts that the subscriber receives four *livekit.SipDTMF packets with the expected codes and digits in order. It also checks the publisher’s WebRTC GetStats for four messages on the _reliable data channel and none on _lossy.

• The updated integration test passed against a local LiveKit server with CGO_ENABLED=0.
• mage test, which includes -race, passed locally before this API simplification. The latest full-suite attempt was blocked by a missing local soxr dependency.

Notes

• The helper sends DTMF digits to all participants in the room.
• Reliable delivery matches the other SDKs.

[CLAassistant]

All committers have signed the CLA.

[cnderrauber]

There are no options for publishing dtmf in other sdks, so go-sdk doesn't need options too.

[ayukumar261]

Thanks for reviewing! I removed the opts argument from the helper.

However, I was looking at the Rust SDK publish_dtmf helper, and it includes destination_identities for destination support. If you think I should add a destinationIdentities... argument for the Go SDK PublishDTMF helper, please let me know!