fix(core): prevent timer/ticker leaks; use unsafe.Add for pointer arithmetic

[eileenaaa]

Description

This PR improves runtime safety and resource handling:

• Timer: replaced time.After(...) with time.NewTimer(...) and ensured timer.Stop() is always called to avoid hidden leaks in loops.
• Ticker: added ticker.Stop() and refactored time.Tick(...) usage to use time.NewTicker for proper lifecycle management.
• Unsafe pointer: switched from unsafe.Pointer + uintptr(offset) to unsafe.Add(...) for clearer and more consistent pointer arithmetic.

These changes make timer/ticker usage safer in long-running goroutines and align pointer operations with modern Go practices.

Checklist

• Code compiles correctly and linting passes locally
• For all code changes, an entry added to the CHANGELOG.md file describing and linking to
  this PR
• Tests added for new functionality, or regression tests for bug fixes added as applicable