Add pokemon form trigger conditions

[dyp1109]

Change description

Addressing issues #1549 by adding new form triggers fields in /api/v2/pokemon-form/ endpoints.

Changes included:

• New PokemonFormMethod and PokemonFormCondition models to store how a form is activated,
• New pokemon_form_methods.csv to define trigger types, and pokemon_form_conditions.csv to link forms to their trigger methods.
• New za mega-stones in items.csv

AI coding assistance disclosure

I use AI assistant for formatting.

Contributor check list

• I have written a description of the contribution and explained its motivation.
• I have written tests for my code changes (if applicable).
• I have read and understood the AI Assisted Contribution guidelines.
• I will own this change in production, and I am prepared to fix any bugs caused by my code change.

[Naramsim]

Hi, can you merge the migrations into a single one?

Can you address the failing tests?