fix(battle): DoubleOnly trainers no longer set to single battle after reload

[Jimmybald1]

What are the changes the user will see?

Twins and other DoubleOnly trainers were being set to single battle when loading from a session.

Why am I making these changes?

They should not be single battles. Ever.

What are the changes from a developer perspective?

Added a .doubleOnly check to the existing .hasDouble check.

Screenshots/Videos

Twins

Before

Before changes, after refreshing and loading from a session:

After

After changes, after refreshing and loading from a session:

How to test the changes?

This seed has Twins on Wave 5:

const overrides = {
  STARTING_WAVE_OVERRIDE: 5,
  STARTING_BIOME_OVERRIDE: BiomeId.PLAINS,
  DAILY_RUN_SEED_OVERRIDE: "adsfasdfddds",
} satisfies Partial<InstanceType<OverridesType>>;

New Game > Daily Run > fight (see that the Twins throw out 2 enemies and you're in a double battle)
Refresh browser > Continue > fight (before: single battle, after: still a double battle)

Checklist

• The PR content is correctly formatted:
  • I'm using beta as my base branch
  • The current branch is not named beta, main or the name of another long-lived feature branch
  • I have provided a clear explanation of the changes within the PR description
  • The PR title matches the Conventional Commits format (as described in CONTRIBUTING.md)
• The PR is self-contained and cannot be split into smaller PRs
• There is no overlap with another open PR
• The PR has been confirmed to work correctly:
  • I have tested the changes manually
  • The full automated test suite still passes (use pnpm test:silent to test locally)
  • I have created new automated tests (pnpm test:create) or updated existing tests related to the PR's changes if necessary
• I have provided screenshots/videos of the changes (if applicable)
  • I have made sure that any UI changes work for both the default and legacy UI themes (if applicable)

Are there any localization additions or changes? If so:

• I have created an associated PR on the locales repository
  • If so, include a link to the PR here: _____
• I have contacted the Translation Team on Discord for proofreading/translation

Does this require any additions or changes to in-game assets? If so:

• I have created an associated PR on the assets repository
  • If so, include a link to the PR here: _____