Restore removed `getHandStash()` function#2900

Entails fixing the bugs in #2715 which seemingly prompted the function’s removal.

Allowing a script to directly access/modify the hand stash would be useful. For example, something like player.getHandStash().search(player.color) would let a player view their currently stashed cards (although that’s not read-only so maybe use your own UI - future feature request?).

Additionally, right now there’s no way for a script to detect whether a hand has a hand stash (without manually tracking state), so if fixing getHandStash is too complex there should at least be a hasHandStash method or property.

we can look into it further

for the moment, exposing getHandStash is a bad idea, as it remains very buggy (a deck decaying into a single card by having its second-to-last card removed causes quite a few issues)

for now, perhaps consider a non-interactable deck off to the side