Implement local caching of index of CPM bits

Consider indexing plugins at CPM bits repository locally, the same as apt or other tools. This would improve performance on users, that would experience improved search or autocompletion response times.

The issue names no files, tests, or entry points. Start by locating the code that searches or autocompletes the CPM bits repository, then determine how a local index should be stored and refreshed; done means repeated searches or completions use the local cache and remain current.

Written by the indexing model from the issue text.