Fix stream header / SubscribeOk race

[sgodin]

If we receive a stream header with an unknown track alias, then wait for up to 1 second for SubscribeOk to arrive

-remove panic if Fetch stream header

[Copilot]

Pull request overview

This PR fixes a race condition where stream headers with unknown track aliases could arrive before the corresponding SubscribeOk message. The solution introduces a notification-based waiting mechanism with a 1-second timeout, and also removes a panic when receiving Fetch stream headers by adding proper error handling.

Key Changes:

• Added tokio::sync::Notify to signal when the subscribe alias map is updated
• Refactored get_subscribe_id_by_alias to optionally wait up to 1 second for aliases to appear
• Added early validation to reject non-SUBGROUP stream types with proper error instead of panicking

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
moq-transport/src/session/subscriber.rs	Implements race condition fix with notification-based waiting, adds subscribe alias notification field, refactors get_subscribe_id_by_alias to support async waiting, adds non-SUBGROUP stream type validation, makes recv_datagram async, and fixes spelling error
moq-transport/src/session/mod.rs	Updates recv_datagram call to handle async signature

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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