[Dev] Add overrides for alternating between single and double battles

[PigeonBar]

What are the changes the user will see?

BATTLE_TYPE_OVERRIDE: "even-doubles", - Double battles on even-numbered waves, single battles on odd-numbered waves.
BATTLE_TYPE_OVERRIDE: "odd-doubles", - Double battles on odd-numbered waves, single battles on even-numbered waves.

Ideally, no changes if not using overrides.

Why am I making these changes?

This will help with testing transitions between single and double battles. For example, it will help with testing the newly implemented Commander (#4670).

(I am adding both "even-doubles" and "odd-doubles" so that, for example, we can force a X0 -> X1 biome change to be either a singles -> doubles or doubles -> singles transition.)

What are the changes from a developer perspective?

1. Added code for handling the added override options.
2. Added a test to double-check that these changes do not accidentally affect regular (non-overrides) gameplay.

Screenshots/Videos

even-doubles

20241109.Even.Doubles.mp4

odd-doubles

20241109.Odd.Doubles.mp4

How to test the changes?

Use the above overrides in overrides.ts.
npm run test double_battle.test.ts

Checklist

• I'm using beta as my base branch
• There is no overlap with another PR?
• The PR is self-contained and cannot be split into smaller PRs?
• Have I provided a clear explanation of the changes?
• Have I considered writing automated tests for the issue?
• [ ] If I have text, did I make it translatable and add a key in the English locale file(s)?
• Have I tested the changes (manually)?
  • Are all unit tests still passing? (npm run test)
• [ ] Are the changes visual?
  • Have I provided screenshots/videos of the changes?

[MokaStitcher]

haven't playtested but code lgtm

[torranx]

DoubleType is now SingleOrDoubleType, hope everyone's happy now

TBH, I still prefer BattleMode or the one Moka mentioned, BattleStyle. SingleOrDoubleType to me is like naming DayOrNight for day and night types which I personally don't like

EDIT: if we decide to keep the SingleOrDoubleType, at least remove the "Type" from the name 👍

[DayKev]

Since BattleType is unfortunately already taken, BattleStyle seems good.

[torranx]

lgtm, would love to see another pr that changes the battyleType override to battleStyle for consistency