fix: remove implicit dependency on unenv

[danielroe]

Types of changes

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

Description

we're moving away from unenv for mocking as it can cause issues with hoisting (and current code won't work with unenv v2 (and this module doesn't have unenv as a dep)

also spotted that defu wasn't an explicit dependency either

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)