NPC trade - bugfixes and improvements

[RoyBerube]

Summary

Bugfixes "NPC trade dupe fix and other fixes"

Purpose of change

Fixes #50454 Fixes #46874 Fixes #49209 Fixes #47939 Item duplication when trading with NPC or merchant

Fixes #46765 Ammo in belts and magazines not included in trade value.

Fixes #42432 Fixes #40175 NPC trade volume and weight not properly updating.

Describe the solution

Disallows trading an item twice in two ways:

1. All non worn containers are collapsed so only the container is listed. This also helps to simplify the trade list for item selection.
2. Worn containers will list their contents as well as the container. The container price is just for itself, and can be traded by itself without any contents being included. Contents can be included or excluded at will. No duplication is possible.

Some logic was checking the item location the wrong way and resulted in weight and volume updates being incorrect.

Ammo in belts and magazines is now priced correctly as a byproduct of code changes.

Describe alternatives you've considered

Rewriting the trade interface. It would be better imo to behave more like the AIM or inventory screen for selection.

Testing

Full test program found no problems.

Tested with NPC ally and NPC merchant. Assorted weapons, tools, kits, containers, stacked items, liquids, ammo, worn canteen. Trading and pricing seems to be working consistently and correctly.

Additional context

[Night-Pryanik]

Why did you revert my edit to your OP? Doesn't your PR fixes all these issues?

[PatrikLundell]

Just a sanity check: I assume you're not allowed to trade away closed containers alone, in particular when the contents are liquid.
"Hey Mr. Merchant, I have here this nice locked safe I want to sell to you"...

[RoyBerube]

Why did you revert my edit to your OP? Doesn't your PR fixes all these issues?

Sorry, I didn't realize you had edited it. Won't happen again.

[Maleclypse]

Roy would you be interested in making an NPC trait or other change so that “Merchant” NPCs will never sell an item for less than 115% of its post_apoc_price and never buy for more than 85% of its post_apoc_price?

[RoyBerube]

Roy would you be interested in making an NPC trait or other change so that “Merchant” NPCs will never sell an item for less than 115% of its post_apoc_price and never buy for more than 85% of its post_apoc_price?

Cataclysm-DDA/src/npctrade.cpp

Line 131 in af27432

double npc_trading::net_price_adjustment( const Character &buyer, const Character &seller )

Clamping is already done there, so it would not take much to change the clamp value according to some json setting. I'm not that familiar with the npc json files so cannot comment on that part.