[Balance] No more double 50x bosses in Endless + cleaning up RNG

[frutescens]

What are the changes the user will see?

Wave 50x bosses will no longer be encountered as double battles.
Little to no impact on Endure Tokens + Thief/Covet however.

Why am I making these changes?

Balance request.

What are the changes from a developer perspective?

New conditional added to battle-scene.ts that cancels out a double battle if it is a wave 50x boss battle.
Endure Token RNG brought into standard format with the rest of the game. It no longer relies on percentages (0.02 -> 2) and RandSeedInt(100) is used to determine the target's endure chance instead. This ensures that the Endure token is tied to the current battle's seed, not the overall run's seed. Also brought in Thief/Covet chance rolls to be in line with the game too.

How to test the changes?

1. Endless bosses should no longer generate as doubles on floors 50, 100, 150...
2. Test Endure Token behavior and report changes.
3. Test Covet/Thief and report changes.

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 tested the changes (manually)?
  • Are all unit tests still passing? (npm run test)

[PigeonBar]

It turns out there's an old bug with the isEndlessBoss() function, this should be return waveIndex % 50 === 0 && ... instead. Thankfully isEndlessBoss() is not used anywhere else in the code.

pokerogue/src/game-mode.ts

Lines 238 to 241 in 0c521bb

	isEndlessBoss(waveIndex: integer): boolean {
	return !!(waveIndex % 50) &&
	(this.modeId === GameModes.ENDLESS || this.modeId === GameModes.SPLICED_ENDLESS);
	}

[PigeonBar]

Partially fixes #4527 for endure tokens.