Remember approved installer scripts to simplify package upgrades

Arch Linux has a similar user managed package installer, and resultant similar security considerations. One feature which I've rather liked in [pacaur](https://github.com/rmarquis/pacaur) (huh, maintainer just recently dropped it) is that it remembers which `PKGBUILD` scripts I've already approved. If the script hasn't changed, it continues without asking if I'd like to review it (since I've already seen it and approved), and if the script has changed, it shows me just the differences which have changed to review and approve. This saves me quite a bit of time when updating packages, without reducing security in any appreciable degree (yes, might see something on the second pass, but are more likely to carefully review the first pass if confident it _is_ the first pass - so maybe slightly _increases_ security).

Please add this time saving feature to `choco`:
- remember approved install scripts
- if unchanged, proceed without asking by default (or at least have a flag/option to enable this)
- if changed, show only the diff to approve (something like `diff -u` w/default 5 lines of context should be good)

Thank you for providing a real package manager for Windows applications.

No files, tests, or entry points are named. Begin by locating Chocolatey's installer-script approval flow and its tests, then define how approved scripts are identified, persisted, compared, and reviewed; done means unchanged approved scripts can skip prompts and changed scripts show a reviewable diff with an approval path.

Written by the indexing model from the issue text.