Move `Time t` from `TEntry` to `TStorageItem`

This may be cleaner because it allows us to infer names purely based on a storage item. On the other hand, it makes location extraction for name generation more difficult, because the pre- and the post-versions of each location will become separate location values which need to be matched to generate the correct assertions.

Start by locating the definitions of TEntry and TStorageItem, then trace location extraction and name generation. Determine how moving Time affects matching pre- and post-versions and the assertions generated; the work is done when storage-item names and those assertions remain correct.

Written by the indexing model from the issue text.