rtc2rtmp: Support RTC-to-RTMP remuxing with HEVC. v7.0.43 (#4349)

**Introduce**

This pull request builds upon the foundation laid in
https://github.com/ossrs/srs/pull/4289 . While the previous work solely
implemented unidirectional HEVC support from RTMP to RTC, this
submission further enhances it by introducing support for the RTC to
RTMP direction.

**Usage**

Launch SRS with `rtc2rtmp.conf`

```bash
./objs/srs -c conf/rtc2rtmp.conf
```

**Push with WebRTC**

Upgrade browser to Chrome(136+) or Safari(18+), then open [WHIP
encoder](http://localhost:8080/players/whip.html?schema=http&&codec=hevc),
push stream with URL that enables HEVC by query string `codec=hevc`:

```bash
http://localhost:1985/rtc/v1/whip/?app=live&stream=livestream&codec=hevc
```

This query string `codec=hevc` is used to select the video codec, and
generate lines in the answer SDP.

```
m=video 9 UDP/TLS/RTP/SAVPF 49 123
a=rtpmap:49 H265/90000
```

The encoder log also show the codec:

```
Audio: opus, 48000HZ, channels: 2, pt: 111
Video: H265, 90000HZ, pt: 49
```

**Play with RTMP**

Play HEVC stream via RTMP.

```bash
ffplay -i rtmp://localhost/live/livestream
```

You will see the codec in logs:

```
  Stream #0:0: Audio: aac (LC), 48000 Hz, stereo, fltp
  Stream #0:1: Video: hevc (Main), yuv420p(tv, bt709), 320x240, 30 fps, 30 tbr, 1k tbn
```

You can also use [WHEP
player](http://localhost:8080/players/whep.html?schema=http&&codec=hevc)
to play the stream.

Important refactor with AI:

* [AI: Refactor packet cache for RTC frame
builder.](b8ffa1630e)
* [AI: Refactor the packet copy and free for
SrsRtcFrameBuilder](f3487b45d7)
* [AI: Refactor the frame detector for
SrsRtcFrameBuilder](4ffc1526b9)
* [AI: Refactor the packet_video_rtmp for
SrsRtcFrameBuilder](81f6aef4ed)
* [AI: Add utests for
SrsCodecPayload.codec](61eb1c0bfc)
* [AI: Add utests for VideoPacketCache in
SrsRtcFrameBuilder.](fd25480dfa)
* [AI: Add utests for VideoFrameDetector in
SrsRtcFrameBuilder.](b4aa977bbd)
* [AI: Add regression test for RTC2RTMP with
HEVC.](5259a2aac3)

---------

Co-authored-by: Jacob Su <suzp1984@gmail.com>
Co-authored-by: winlin <winlinvip@gmail.com>

.gitignore

@@ -42,4 +42,5 @@ cmake-build-debug
 /trunk/ide/srs_clion/srs
 /trunk/ide/srs_clion/Testing/
 /trunk/ide/vscode-build
+/build/