Cargo can buy more presents at Christmas time (#94251)

## About The Pull Request

Last Christmas we had and resolved this bug #88595 where via the
mechanic of buying random trash, Cargo could roll on the roulette to try
and get random Christmas presents and open them for random items.
This was removed because it's not supposed to work that way and was a
way of exploiting Christmas cheer for personal gain, which is grinchsome
behaviour.

That said, being able to order Christmas presents is also kind of
soulful, so this PR brings that mechanic back but on purpose this time.

During the Christmas season _only_, Cargo can spend 3000 credits of
their budget to order a "Surplus Christmas Gifts" crate which contains
4-6 presents _with pre-assigned recipients_.
In a similar system to addressed mail, only the person written on the
gift tag can open the present, so unless you're sufficiently scroogeous
to collect a huge pile of presents on the cargo room floor in hopes of
getting a couple with your name on (in my testing these contained raw
unbaked croissant dough, and a piece of paper from a space ruin) you
should mostly be using this to deliver generalised holiday cheer to the
crew rather than just yourself.



This PR also contains (maybe as more lines than the actual feature) a
refactor changing a bunch of boolean vars on `/datum/supply_pack` into
bitflags, because I needed to add one more and it seemed silly to have
so many booleans.

## Why It's Good For The Game

It allows those with the yuletide spirit to deliver some christmas cheer
to their fellow man, isn't that the season's reason?

## Changelog

🆑
add: When the game considers it to be Christmas, Cargo can order
additional Christmas gifts pre-addressed to random crew members.
/🆑

code/__DEFINES/cargo.dm

@@ -41,6 +41,28 @@
 ///Used by coupons to define that they're cursed
 #define COUPON_OMEN "omen"
 
+// Supply pack flags determining ordering properties
+/// Order is literally never visible, presumably it's an abstract type or something
+#define ORDER_INVISIBLE (1 << 0)
+/// Only orderable on emagged consoles
+#define ORDER_EMAG_ONLY (1 << 1)
+/// Only orderable on consoles with doctored boards
+#define ORDER_CONTRABAND (1 << 2)
+/// Can only be ordered privately, can use discount coupons, and arrives in a bag instead of a crate
+#define ORDER_GOODY (1 << 3)
+/// Can only be ordered via the express order console
+#define ORDER_POD_ONLY (1 << 4)
+/// Can only be ordered if the following flag is also enabled, for conditionally provided options
+#define ORDER_SPECIAL (1 << 5)
+/// If present then a special order can be ordered
+#define ORDER_SPECIAL_ENABLED (1 << 6)
+/// Unavailable to departmental order consoles even if it is in an appropriate category
+#define ORDER_NOT_DEPARTMENTAL (1 << 7)
+/// This will notify admins when it is purchased
+#define ORDER_DANGEROUS (1 << 8)
+/// This is set when something is created by an admin to make sure its contents is also marked as such
+#define ORDER_ADMIN_SPAWNED (1 << 9)
+
 ///Discount categories for coupons. This one is for anything that isn't discountable.
 #define SUPPLY_PACK_NOT_DISCOUNTABLE null
 ///Discount category for the standard stuff, mostly goodies.