tree b7c1c50aa2b3f8f1b4850cd0848776c0bea1460e
parent b0e6aa46401841a9843a3a0642f654284c945273
author martinduke <martinduke@google.com> 1784303276 -0700
committer Copybara-Service <copybara-worker@google.com> 1784303313 -0700

Move SUBSCRIBE to a dedicated bidirectional stream.

This change refactors MoQT to handle SUBSCRIBE messages on their own bidirectional streams, rather than on the control stream.

Key changes include:
-   New `MoqtSubscribeRequestStream` and `MoqtSubscribeResponseStream` classes.
-   `MoqtSession::Subscribe` now opens a bidi stream and sends the SUBSCRIBE message on it.
-   `MoqtSession::Unsubscribe` now resets the bidi stream associated with the subscription.
-   `MoqtSession::RequestUpdate` sends the update on the existing subscribe bidi stream.
-   The control stream no longer processes SUBSCRIBE, SUBSCRIBE_OK, or UNSUBSCRIBE messages.
-   `MoqtUnsubscribe` message type and serialization/parsing are removed.
-   MoqtSession no longer owns any subscriptions
-   All external state is now destroyed in Detach(). On teardown, streams are destroyed in arbitrary order, making clearing such state in the destructor dangerous.

I wrote better helper functions in MoqtSessionTest to reduce the toil in sending/receiving messages, setting up bidi streams, and not hard-coding message formats.

PiperOrigin-RevId: 949593252