Fixup/renameinvalidate

[willscott]

simplify to remove inverse cache and directly invalidate handles

[DUOLabs333]

This doesn't fix the problem of handles not being one-to-one/a new handle is returned every lookup.

[willscott]

Good point. I think we do need the complexity you suggested. I added an additional method to properly evict from the reverse index as well.

[DUOLabs333]

Technically, the reverse cache must also hold the filesystems --- at which point, we should just use my PR.

[willscott]

does it?

• if the handle matches, you can recover the filesystem from the forward cache
• I'd prefer a single strong type rather than any for the value
• we should be doing expiry so that the reverse cache doesn't grow in an unbounded way