Improve ergonomics of platform_support's Instant

[Mathspy]

Objective

• Make working with bevy_time more ergonomic in no_std environments.

Currently bevy_time expects the getter in environments where time can't be obtained automatically via the instruction set or the standard library to be of type *mut fn() -> Duration. fn() is already a function pointer, so *mut fn() is a pointer to a function pointer. This is harder to use and error prone since creating a pointer out of something like &mut fn() -> Duration when the lifetime of the reference isn't static will lead to an undefined behavior once the reference is freed

Solution

• Accept a fn() -> Duration instead

Testing

• I made a whole game on the Playdate that relies on bevy_time heavily, see: bevydate_time for usage of the Instant's getter.

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Showcase

Click to view showcase

test2.mp4

Migration Guide

This is a breaking change but it's not for people coming from Bevy v0.15

Small thank you note

Thanks to my friend https://github.com/repnop for helping me understand how to deal with function pointers in unsafe environments

[github-actions]

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[bushrat011899]

Yeah that is better, thanks for submitting this! And thanks for confirming that the Playdate works too!

[Mathspy]

Yeah that is better, thanks for submitting this! And thanks for confirming that the Playdate works too!

Thank YOU for all the hard work championing Bevy's no_std support in such a short time ❤️ I was really excited when I saw #15460 a few months ago when I ordered my Playdate and couldn't wait to run Bevy on it

[BD103]

The changes look good, and the demo video was super cool! (Now I want a Playdate ^^)