changed: Break non-async specific interrupt functionality out of async_hal module

[jbeaurivage]

Summary

In preparation for #804, we realized that the async_hal::interrupts module contained interrupt-related functionality that wasn't strictly specific to async operation. Break that out into its own interrupt module, so that it can be used even in non async contexts.

Checklist

• All new or modified code is well documented, especially public items
• No new warnings or clippy suggestions have been introduced