use // INTERVALS_PER_SLOT for store.time slot calculations

[unnawut]

🗒️ Description

• Fixes following fix: correct interval calculation in tick_interval method #222 (thanks @crStiv) in a few more places where the code still assumes store.time is stored as seconds
  • For reference, store.time is "intervals since genesis" as documented on the class definition and originally in the markdown specs
• Adding TestGetForkchoiceStore as test cases for fix: correct interval calculation in tick_interval method #222
• Removing TestSlotTimeCalculations that's not testing actual code

🔗 Related Issues or PRs

Relates to #222

✅ Checklist

• Ran tox checks to avoid unnecessary CI fails:

  uvx tox

• Considered adding appropriate tests for the changes.
• Considered updating the online docs in the ./docs/ directory.

[tcoratger]

Thanks for the fix, just a minor comment.

[tcoratger]

Here in the computations instead of having the hardcoded numbers, can't we use INTERVALS_PER_SLOT so that this will resist changes in the constant?

[unnawut]

Sounds good. Also made it property-based now so it doesn't stick to just the same slots: bad1d29