v0.8.3

Upgrading: databases migrate automatically on first start.

Added

• Storage stall and I/O pressure telemetry in the flight recorder and
  historical databases (#16):
  • iowait_pct: CPU time spent waiting on disk I/O, separated from idle time
    in /proc/stat.
  • procs_blocked: count of processes currently waiting for I/O (nr_iowait).
  • dirty_kb: uncommitted dirty writeback memory from /proc/meminfo.
  • psi_io_some and psi_io_full: 10-second rolling averages from Linux
    Pressure Stall Information (/proc/pressure/io), falling back to None on
    kernels built without CONFIG_PSI.