Address an issue where `OldestAsyncManager` instances created before forking resulted in each child process maintaining its own isolated copy-on-write stats, leaving the parent process with an empty/unused instance. This caused the final `dump_recon` call at the end of `run_forever` to report no meaningful telemetry.
The fix aggregates per-disk recon stats collected by each child process. This is done by loading recon cache data from all devices, consolidating key metrics, and writing the aggregated stats back to the recon cache.
Change-Id: I70a60ae280e4fccc04ff5e7df9e62b18d916421e
af57922cd8