Port the code from Insomnia.swift into the iOS platform channel

> Also, iOS has known issues where it may not keep the screen on (affecting 16.4 and higher). Once I get myself an iOS device, I'm gonna port the code from [Insomnia.swift](https://github.com/ochococo/Insomnia/blob/master/Insomnia/Insomnia.swift) into the iOS platform channel. The emulator may not be ideal for testing the wakelock.

_Originally posted by @diegotori in [#59](https://github.com/fluttercommunity/wakelock_plus/issues/59#issuecomment-2106072156)_