A record-enabled camera whose record stream produces no cache segments
never appears in grouped_recordings, so the per-camera prune in
RecordingMaintainer.move_files() never runs for it. Its
object_recordings_info and audio_recordings_info buffers then grow
without bound until the recording process is OOM-killed (discussion
#23451).
Run a prune every move_files() cycle for cameras absent from
grouped_recordings, dropping entries older than the longest a segment
could still wait in cache before being matched
(MAX_SEGMENTS_IN_CACHE * MAX_SEGMENT_DURATION * 2). Cameras present in
grouped_recordings are left untouched and keep their existing prune.
Add a regression test asserting that an absent camera's stale entries
are dropped (recent ones kept) while a present camera's entries are
left intact.
