[QoL] Add fusion options to overrides

[EmberCM]

What are the changes?

Create override options for starter fusions and enemy fusions

Why am I doing these changes?

Make testing easier

What did change?

Added options in the overrides.ts for fusions

export const STARTER_FUSION_OVERRIDE: boolean = false;
export const STARTER_FUSION_SPECIES_OVERRIDE: Species | integer = 0;
export const OPP_FUSION_OVERRIDE: boolean = false;
export const OPP_FUSION_SPECIES_OVERRIDE: Species | integer = 0;

Screenshots/Videos

STARTER_FUSION_OVERRIDE

STARTER_FUSION_SPECIES_OVERRIDE

OPP_FUSION_OVERRIDE

OPP_FUSION_SPECIES_OVERRIDE

How to test the changes?

Change the new options in overrides.ts

Checklist

• 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)
• Are the changes visual?
  • Have I provided screenshots/videos of the changes?

[flx-sta]

Could you also prepare the method in overridesHelper.ts please?