Handle cache invalidation for @latest versions in multibundles

When i do `console.log(require('mercury').h)` in requirebin, it prints an old version of `h`

It looks like this is a cache invalidation problem or an issue of getting the wrong mercury.

Maybe this is a problem in wzrd.in

Maybe this is an issue with requirebin accepting any version of mercury.

It would be nice to:
- always get latest
- see which version i get in requirebin
- have a cache bust opt in

This is also a requirebin UI issue.

Placing this issue here since I think the root cause is cache invalidation.

cc @maxogden @jesusabdullah

No files or tests are named. Start by reproducing the requirebin case with console.log(require('mercury').h), then trace how @latest versions are resolved and cached across wzrd.in and the requirebin UI. Done should include reliable latest-version behavior, visible version information, and an agreed cache-busting option.

Written by the indexing model from the issue text.