updates the Validators.Base.CheckerFunction typing to be more strict,…

[fugufish]

… this potentially saves some debuggin hours when implementing a custom validator

📝 Description

This fixes difficulties when writing a custom validator in typescript by strenghening the typings around the CheckerFunction. The stronger typing allows errors in how validators are implemented to be detected earlier.

💎 Type of change

• New feature (non-breaking change which adds functionality)

🚦 How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Tested against a custome validator for Yup

🏁 Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas