fix: update lastExecution on actual execution

[Abhi-05-git]

Description

Updates lastExecution when the callback actually begins execution, so skipped ticks caused by waitForCompletion do not incorrectly advance the execution timestamp.

Related Issue

Fixes #1048.

Motivation and Context

When waitForCompletion is enabled and a previous callback is still running, a scheduled tick can be skipped. lastExecution should represent the last actual callback execution rather than a skipped tick.

How Has This Been Tested?

Added a regression test covering waitForCompletion and lastExecution behavior.

• npm test -- --runInBand — 162 tests passed
• npm run build — passed

Screenshots (if appropriate)

Not applicable.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• If my change introduces a breaking change, I have added a ! after the type/scope in the title.