Support for collecting timings from threads, and implement async task timings (#6333)

The following callbacks can now be registered in timings, to allow threads to be notified of these events:
- Turning on/off (`TimingsHandler::getToggleCallbacks()->add(...)`)
- Reset (`TimingsHandler::getReloadCallbacks()->add(...)`)
- Collect (`TimingsHandler::getCollectCallbacks()->add(...)`)

Collect callbacks must return `list<Promise>`. The promises must be `resolve()`d with `list<string>` of printed timings records, as returned by `TimingsHandler::printCurrentThreadRecords()`. It's recommended to use 1 promise per thread.

A timings report will be produced once all promises have been resolved.

This system is used internally to collect timings for async tasks (closes #6166).

For timings viewer developers:
Timings format version has been bumped to 3 to accommodate this change. Timings groups should now include a `ThreadId`  at the end of timings group names to ensure that their record IDs are segregated correctly, as they could otherwise conflict between threads. The main thread is not required to specify a thread ID. See pmmp/timings@13cefa6279 for implementation examples.

New PHPStan error is caused by phpstan/phpstan#10924

tests/phpstan/configs/phpstan-bugs.neon

@@ -90,6 +90,11 @@ parameters:
 			count: 1
 			path: ../../../src/plugin/PluginManager.php
 
+		-
+			message: "#^Method pocketmine\\\\timings\\\\TimingsHandler\\:\\:lazyGetSet\\(\\) should return pocketmine\\\\utils\\\\ObjectSet\\<T of object\\> but returns pocketmine\\\\utils\\\\ObjectSet\\<object\\>\\.$#"
+			count: 1
+			path: ../../../src/timings/TimingsHandler.php
+
 		-
 			message: "#^Casting to int something that's already int\\.$#"
 			count: 1