EP-08 Design app with thread-safe frame record accumulation

[Adityasakare]

Implement FrameRecord and ProfilerData structures which use std::mutex for the frame vector and std::atomic for counters. GStreamer pad probes run on streaming threads.

Why

Without thread safety, concurrent probe callbacks corrupt the frame vector. std::atomic for counters avoids lock overhead on hot path.

Acceptance criteria

• FrameRecord: frame_number, enter_ns, exit_ns, latency_ms, encoded_bytes, is_keyframe
• ResourceSnapshot: timestamp_ns, cpu_percent, rss_kb
• ProfilerData: vector with std::mutex
• std::atomic frame_count
• add_frame() method thread-safe
• No data races (run with -fsanitize=thread)

Resources

• std::atomic cppreference
• GST_BUFFER_FLAG_DELTA_UNIT