Simplify caching of status checks and fixes missing domain_id condition

Simplify caching of status checks and fixes missing domain_id condition

Fixes a few apparent problems:
- domain_id was ommitted causing unexpected results
- Civi::cache was being read but never written to
- Object caching did not persist in memory across different check classes
- If we did write to Civi::cache there is no mechanism for clearing that cache when data changes

Solution: use simple array cache in Civi::$statics