feature: add plugin file date/hash to plugin load messages & logs for auditing

[leondz]

goal

to give the best possible chance of knowing exactly which version/revision of a plugin was used in a given run, from the accompanying log. the easier this is to work out, the better

suggestion

• at garak load,
  • log gh current hash if known
    • in garak.log
    • in report.jsonl
• at plugin load,
  • log file date as info (use same date as the cache uses)