Add Z.ai coding plan support

[daniel-lxs]

Adds support for Z.ai's coding plan subscription tiers (International and China).

Pulled from downstream PR Kilo-Org/kilocode#2402. Thanks @chrarnoldus.

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Important

Add support for Z.ai's new coding plan subscription tiers, updating schemas, configurations, and tests to handle international and China options.

• Behavior:
  • Adds support for Z.ai's new coding plan subscription tiers (international_coding, china_coding) in provider-settings.ts and zai.ts.
  • Updates ZAiHandler in zai.ts to use zaiApiLineConfigs for determining base URL and region.
  • Defaults to international_coding if zaiApiLine is not specified.
• Configuration:
  • Introduces zaiApiLineSchema and zaiApiLineConfigs in provider-settings.ts to manage Z.ai API lines.
  • Updates zaiApiLine handling in ZAi.tsx to reflect new subscription tiers.
• Testing:
  • Updates tests in zai.spec.ts to cover new subscription tiers and default behavior.
  • Ensures correct API key and base URL usage in tests for both international and China configurations.

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