fix: Handling retired or changed scanners

[agittins]

• Refactor _refresh_scanners to be more efficient, and to handle the case where a scanner still exists but is no longer a scanner.
• Refactor coordinator.init() to move callbacks out into class methods.
• Tamed down lots of debug logging
• Altered self.last_config_entry_update to use MONOTONIC_TIME(), and changed cooldown to a const of 10 seconds, and included check for parallel save tasks.
• Removed assert that excluded scanners from area-by-mindist