Migrate to bevy 0.14

[luca-della-vedova]

This PR migrates the crate to 0.14.

I split it in two:

• 15b94d8 does the minimum needed to get the crate to compile without warnings in 0.14
• f07cdb1 Runs cargo fmt on the codebase to clean it up a bit.

Happy to remove the second if needed, I thought it would be nice to get the crate in a clean cargo fmt state

[nilclass]

Thanks for these changes @luca-della-vedova, I've published them as 0.14.0 just now.

I thought it would be nice to get the crate in a clean cargo fmt state

totally agree! I've added cargo fmt --check to the build workflow now, so it stays clean in the future.