refactor(test): replaces chai with node:assert and chai-json-schema with ajv

[sverweij]

Description

• replaces the chai assertion library use with their native node:assert counterparts
• replaces the chai-json-schema chai plugin with a straight use of ajv
• removes chai-json-schema from the manifest as it ain't used no more

The more laborious parts we'll do in a separate PR, likely with the help of a codemod of sorts.

Motivation and Context

• less dependencies to manage
• node:assert ships with node anyway and is good enough™️

How Has This Been Tested?

• green ci

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Documentation only change
• Refactor (non-breaking change which fixes an issue without changing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• 📖

  • My change doesn't require a documentation update, or ...
  • it does and I have updated it

• ⚖️

  • The contribution will be subject to The MIT license, and I'm OK with that.
  • The contribution is my own original work.
  • I am ok with the stuff in CONTRIBUTING.md.