Add AI_FLAG_SEQUENCE_SWITCHING

[Pawkkie]

Description

Floated this in Discord the other day and didn't get a lot of traction one way or the other so I thought I'd PR it and we can discuss from here if need be.

Recently Kasen from the Aqua discord was asking me how hard it'd be to make a flag where:

• The AI always switches in mons after a KO in exactly their party order regardless of other factors (index 1, then 2, etc.)
• U-Turn and other forced switches also always choose the lowest party index available
• Mid-battle switches aren't triggered

This PR implements that functionality in AI_FLAG_SEQUENCE_SWITCHING. I can see five main utilities for a flag like this:

• Battles where the designer wants a fully deterministic experience for both themselves and the user
• Hacks where battles are constructed more in the form of puzzles
• Hacks that balance low difficulty casual runs with deterministically solvable difficult nuzlocke runs
• Hacks that want to approximate the experience of playing Gen 1, which uses this switching order
• Battles with a "narrative", ie. switch in Machop -> Machoke -> Machamp even though Machamp would have been "better" to switch in first

I'm of the opinion that this is worth a flag slot as the behaviour is so radically different from existing AI flags, and it's applicable to niches that are not well served by existing flags. I fully understand though that we're tight on AI flags and need to be discerning about what we choose to add.

I've included tests to make sure the three intended features work correctly, as well as a safety net test to make sure this flag doesn't break forced random switching from Roar and effects like Dragon Tail.

People who collaborated with me in this PR

Kasen had the initial idea, psf came up with the flag name, and Egg had some helpful suggestions for overhauling some of the tests.

Discord contact info

@Pawkkie

[DizzyEggg]

Looking good!

The requested changes are really nitpicks at this points, everything looks good.
Also about your worry here

I fully understand though that we're tight on AI flags and need to be discerning about what we choose to add.

I wouldn't worry about that, we could make it u64 instead of u32 and then you have additional 32 flags to work with.

[Pawkkie]

I wouldn't worry about that, we could make it u64 instead of u32 and then you have additional 32 flags to work with.

Definitely thought this would mean a bitfield refactor, super good to know :D

Ready for re-review!