Fix Folia task lifecycle during reload

[Minecraft0122]

Summary

• invalidate callbacks created by an earlier Folia plugin lifecycle so they cannot execute after cancelAllKnownTasks() during reload
• wait for already-running Folia tasks before cancellation returns, while allowing cancellation from inside the current task without deadlocking
• convert async scheduler delays from ticks to milliseconds with TimeAmount.ticksToMillis instead of dividing ticks by 20
• keep the behavior in the shared Folia platform layer, so Plan and other PAL consumers do not need plugin-specific scheduler implementations

Tests

• old-lifecycle callbacks are ignored and new-lifecycle callbacks still execute
• cancellation waits for a running task to finish
• cancellation initiated by the running task does not deadlock
• 20/40/60 ticks map to 1000/2000/3000 milliseconds for asynchronous scheduling
• JAVA_HOME=C:\Program Files\Java\jdk-21 ./gradlew :api:check :folia:check --rerun-tasks passes locally

Context

This moves the Folia scheduling portion of plan-player-analytics/Plan#4772 into PAL as requested by review. It addresses plan-player-analytics/Plan#4599 without adding a Plan-specific platform layer.

The repository-wide check currently stops in the untouched BungeeCord module because net.md-5:brigadier:1.0.16-SNAPSHOT is no longer resolvable; the affected api and folia checks pass.