SCReAM v2: Parse TransportPacketsFeedback once into ScreamFeedback

This CL introduces the ScreamFeedback struct, allowing SCReAM v2 to parse
feedback messages exactly once in ScreamV2::OnTransportPacketsFeedback
and pass the parsed structure to other subcomponents (LossEstimator and
DelayBasedCongestionControl).

This eliminates multiple redundant packet loops, O(N log N) sorting passes,
and vector heap allocations per incoming feedback message.

Bug: webrtc:447037083
Change-Id: I53750f4600cb8f0032dae64a956935a10440371e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/476700
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47861}