Split RTCP compound packet before forwarding

[boks1971]

Split RTCP compound packet before forwarding

When a compound RTCP packet is received, it is forwarded as is to the
read streams. Downstream components have to check for the SSRC in the
packets matching the track(s) it is handling.

This leads to situations where downstream components could see duplicate
RTCP reports. Happens when there is a downstream handler for all SSRCs.
It receives the compound packet, unmarshals it and invokes the handlers.
As it is fielding all SSRCs, it will get the same compound packet `n`
times and invoke the handlers `n` times.

This PR splits up the compound packet and forwards individual packets to
avoid the end handlers from seeing duplicates. API wise, it is
compatible as it still emits an encoded/marshaled packet. But, this does
add a marshaling step.

Packets that have no destination SSRC of their own (e.g. unknown packet
types parsed as rtcp.RawPacket, or receiver reports with no reception
reports) are delivered to every stream the compound packet is addressed
to, instead of being dropped. Such packets can still be seen once per
compound packet by each of those streams, matching the old behavior.

Add unit tests. Before this change, the compound packet test fails at
the point where the test tries to read the CNAME packet and sees an
incorrect type, and the empty destination SSRC test blocks forever
waiting for the rtcp.RawPacket to be forwarded.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.62%. Comparing base (1cd193a) to head (4042833).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #359      +/-   ##
==========================================
+ Coverage   82.54%   83.62%   +1.08%     
==========================================
  Files          19       19              
  Lines        1472     1484      +12     
==========================================
+ Hits         1215     1241      +26     
+ Misses        142      135       -7     
+ Partials      115      108       -7     

Flag	Coverage Δ
go	83.62% <100.00%> (+1.08%)	⬆️

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[Copilot]

Pull request overview

This PR changes SRTCP inbound RTCP handling to split compound RTCP packets and forward the individual RTCP packets to the appropriate read streams, reducing downstream duplication when handlers subscribe broadly.

Changes:

• Update RTCP decrypt/forwarding logic to Unmarshal compound RTCP, then re-Marshal and forward each contained packet separately.
• Add routing behavior for packets with empty DestinationSSRC() (e.g., rtcp.RawPacket) to be forwarded to the compound packet’s addressed SSRC set.
• Add unit tests covering compound packet splitting, empty-destination forwarding, and decrypt error paths.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
session_srtcp.go	Splits decrypted compound RTCP into individual packets and forwards them per-destination (with special handling for empty-destination packets).
session_srtcp_test.go	Adds tests validating per-packet forwarding behavior and error handling scenarios introduced by the new remarshal step.

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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.