perf(video): 优化视频流水线并统一使用 vendored OpenSSL

使用固定采集、解码和编码线程及同步最新帧槽，减少同步异步跨界和无效 MJPEG 解码。

编码前预留消费者容量，以完整批次投递编码结果并隔离慢客户端，避免丢失 H.264 参考帧；保留 PTS 修正，不增加 IDR 节流。

复用 Annex-B 缓冲并增加低频发送分项统计，默认启用 vendored OpenSSL SRTP AES-CM 后端。

HTTP 客户端、HTTPS 服务端和本地 DTLS 证书验证迁移至 OpenSSL，移除 rustls TLS 引擎依赖，保留证书验证、媒体加密和原有协议协商。

vendor/dtls/LICENSE-MIT

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 WebRTC.rs
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.