Python wheels from extensions were not being removed after
install/uninstall in some cases - although installing an extension
afterwards that used wheels would recalculate deps & remove them.
- Installing an extension didn't include the extension in the
compatibility-cache, causing uninstalling not to remove deps.
- Uninstalling an extension wasn't re-calculating the deps,
leaving them as-is.
Always write the compatibility-cache after installing and uninstalling
so changes are detected & handled.
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