Add priority heap and timers implementation (reworked from timers gem).

[ioquatix]

I'd like to expose a native implementation of this for performance reasons. Additionally, we might expose some higher level constructs in the selector, for scheduling timers.

Types of Changes

• New feature.

Contribution

• [x] I added tests for my changes.
• [x] I tested my changes locally.
• [x] I agree to the Developer's Certificate of Origin 1.1.