Immediately apply deferred system params in System::run

[james7132]

Objective

Fixes #11821.

Solution

• Run System::apply_deferred in System::run after executing the system.
• Switch to using System::run_unsafe in SingleThreadedExecutor to preserve the current behavior.
• Remove the System::apply_deferred in SimpleExecutor as it's now redundant.
• Remove the System::apply_deferred when running one-shot systems, as it's now redundant.

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Changelog

Changed: System::run will now immediately apply deferred system params after running the system.

Migration Guide

System::run will now always run System::apply_deferred immediately after running the system now. If you were running systems and then applying their deferred buffers at a later point in time, you can eliminate the latter.

// in 0.13
system.run(world);
// .. sometime later ...
system.apply_deferred(world);

// in 0.14
system.run(world);

[alice-i-cecile]

Much simpler. Feel free to merge once you get CI passing.

[hymm]

Is this going to mess up pipelined rendering extract schedule if you run all the schedules single threaded? i.e. that schedule needs to skip applying it's buffers until it's moved to the render thread.

[james7132]

That would likely be a performance regression. That said I'm not sure why one would be running pipelined rendering with a single threaded executor. It seems counter intuitive.

[hymm]

For lower core systems like quest or switch that only have 3 cores available. The perf you get from pipelining will be worth it. But the overhead from running your schedule multi threaded won't be

[james7132]

@JoJoJet I think that's good enough justification to not deprecate the SimpleExecutor and retain the behavior in the single threaded executor. Thoughts?