Draft: Add saving zbuffer pool

This patch adds control over CtSaving ZBuffer allocation. It proposes the use of a BufferPool in order to make the ZBuffers persistent. It has the following main goals:

• Since malloc_trim(0) is called on every prepare all the previously allocated ZBuffers are released to the OS, imposing an overhead as soon as the first frames are available for compression
• It allows using a NumaAllocator for ZBuffers, which improves overall performance when the processing threads have a specific CPU affinity
• It will allow the release of the main, uncompressed buffer as soon as the compression is finished, doubling the effective capacity of the queue of frames waiting to be saved before an Overrun condition.