revert schedule change for debug render. fixes #496

[Hellzbellz123]

opened as draft cause im not sure if a whole new pr/issue is the way to go

revert schedule change for PhysicsDebugPlugin because it causes large lag

Objective

fixes issue #496
recent scheduling changes from commit 4d082a7 causes PhysicsDebugPlugin too generate lots of lag when enabled

Solution

change default schedule from FixedPostUpdate too PostUpdate

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[Jondolf]

Tested this, and performance for the debug rendering / gizmos indeed seems much worse in fixed timestep schedules 🤔 Having it in PostUpdate should be fine though, thanks for the fix!

For Bevy 0.16, we will likely also start using the retained gizmos added in bevyengine/bevy#15473 for collider debug rendering. It should hopefully improve performance significantly.