Decoupled video buffer from video encoder for more extensibility

[Adonca2203]

This optimization gives the following benefits:

1. Provides a framework where each mode can now implement their own worker for how to handle encoded frames allowing for extension into regular recording and anything else we could want.
2. Further optimizes the workflow, offloading buffer addition to its own worker thread which frees up time on the main encoder thread -- Previously this thread averaged ~20ms on the VAAPI encoder which was horrible; causing the queue to fill up as we weren't popping fast enough. Now it averages 15ms for VAAPI the vaapi workflow which is still cutting it close but I think its just related to all the overhead regarding scaling and such.
3. Renamed the VideoBuffer to better reflect its actual use case