maint: fix global vars creation and all other zsh-sweep reported errors

[psprint]

Description

I've run psprint/zsh-sweep on zinit sources and obtained some reports about global var creation, which were true, so I fixed them.

Motivation and Context

My motivation was testing the linter zsh-sweep on some real-world, complex inputs.

How Has This Been Tested?

I've run zi delete --all and restarted zsh.

Types of changes

• [x] 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 change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[psprint]

I've fixed all errors and made all sources pass zsh-sweep linter. Could the linter be adopted by zinit, @vladdoster ? It would nicely gate the new code for errors.

[vladdoster]

@psprint,

Merge conflicts

[vladdoster]

@psprint,

Is this PR still a WIP?