Complete type annotations of tests/functional/ directory

[jdufresne]

No description provided.

[pradyunsg]

FWIW, for large PRs like this, I'd encourage you to make commits via commit --fixup and doing a single rebase --autosquash once approved, prior to merging. It makes reviewing the actual changes easier. :)

[jdufresne]

Rebasing required several changes to newly added tests and exposed some too strict or loose types elsewhere. I've tried to contain these in the latest fixup commit.

[pradyunsg]

God dammit @jdufresne. Quicker at updating PRs than I am at mentioning that there's a merge conflict.

(seriously though, I really really appreciate that you're keeping these PRs upto date)

[jdufresne]

Rebased and resolved conflicts.

[pradyunsg]

@jdufresne one last time?

[jdufresne]

Resolved conflict in tests/functional/test_install_wheel.py.