[P2][Move] Fix Tera Shell to apply to all hits of multi-strike moves

[innerthunder]

What are the changes the user will see?

Tera Shell now correctly reduces the effectiveness of all hits of multi-strike moves instead of just the first hit.

Why am I making these changes?

closes #4218

What are the changes from a developer perspective?

• field/pokemon: Added new moveEffectiveness field to turnData which caches a move effectiveness value for the current move being used against the associated Pokemon. If not null, this value overrides the output of Pokemon.getMoveEffectiveness(...). This field is currently only used for and modified by Tera Shell's effect.
• data/ability: Tera Shell now changes pokemon.turnData.moveEffectiveness to 0.5 when the ability applies.
• phases/move-effect-phase: now resets target.turnData.moveEffectiveness for all targets of the phase's move on the move's last strike.
• test/abilities/tera_shell.test: New test for Tera Shell covering all hits of a multi-strike move (specifically Double Hit).

Screenshots/Videos

How to test the changes?

npm run test tera_shell (includes new test)

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?

[DayKev]

Could you remove the obsolete ! and comment from L357 in move-effect-phase.ts too please?