Investigate caching password manager operations

[kergoth]

• Some values could be stored in chezmoi.toml. Security is a concern, but as long as it's protected by permissions, it's no less secure than storing these values in their final destinations.
• For binary or larger values, I could probably alter the template to use the existing value. The question becomes how to trigger invalidation of this cache, since it'd bypass the usual chezmoi mechanisms.
• Handling values which are neither an entire file nor a small string could be problematic, for example, subsets of .ssh/config for home and work.

[kergoth]

This is viable, but I haven't made up my mind on whether to actually do it, and cache invalidation would be largely a manual process, though it could be scripted. See https://github.com/kergoth/dotfiles/compare/main...prototype/cached-password-manager for the initial prototype. It's also unlikely to be a recommended practice by the chezmoi community.