Add unit tests for pip and conda package managers

[eleanorjboyd]

The Package pillar of the public API (managePackages, getPackages, refreshPackages) is backed by src/managers/builtin/pipPackageManager.ts and src/managers/conda/condaPackageManager.ts, and neither has a direct unit test. Only their helper utilities (pipListUtils, pipUtils, installArgs, normalizePackageName) and the host-based packageManagement.integration.test.ts provide coverage, so the manager classes' own logic (install/uninstall dispatch, change-event firing, error propagation) is untested at the unit level.

@edvilme you pick to decide exactly how this should look. I think unit test plus some sort of integration test would be ideal.

[edvilme]

Hello, yes! There are a couple of things I want to get polished on the packaging side of things before doing this to make sure all of the package managers behave similarly and that there is a good way of testing this