Track install path type in receipt

Right now, we have some slightly complex logic around path handling with the install prefix. This comes from the fact that we don't know whether it's a cargo home style path or not; cargo home uses an install prefix-style location, with subdirectories, while other methods don't, which means the two methods require slightly different logic. It would be great to replace our current heuristics with actual information we can branch on.

Start by tracing how the receipt is created and how install-prefix paths are currently classified. Compare the cargo home-style and other install methods, then confirm that the receipt records the path type and the existing branching uses that information instead of heuristics.

Written by the indexing model from the issue text.