[Bug][UI/UX] Shiny button can cycle variants even if non-shiny form is uncaught

[Wlowscha]

Why am I making these changes?

When the variant button was removed by #5213, a minor bug was introduced which prevents the player from switching between variants if the non-shiny form is not caught. This has been reported on discord e.g. here. See also these screenshots (from a save where all three variants of Miraidon are unlocked, but the non-shiny form is not): the "cycle shiny" button does not appear.

What are the changes from a developer perspective?

canCycleShiny is now true if at least two variants are caught. The logic for cycling shiny has been reworked to loop correctly ig the non-shiny form is not caught.

Screenshots/Videos

Shiny Miraidon cycling correctly:

Pokerogue.Mozilla.Firefox.2025-03-01.17-42-09.mp4

Proof that the button is still working properly when non-shiny forms are also caught:

Pokerogue.Mozilla.Firefox.2025-03-01.17-45-08.mp4

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)
  • Have I created new automated tests (npm run create-test) or updated existing tests related to the PR's changes?
• Have I provided screenshots/videos of the changes (if applicable)?
  • Have I made sure that any UI change works for both UI themes (default and legacy)?