refactor: Update generated models and adapt to them (#704)

This PR updates the auto-generated Pydantic models based on OpenAPI specification changes in [apify-docs PR #2398](https://github.com/apify/apify-docs/pull/2398).

## Summary

- Regenerated `_models.py` from updated OpenAPI spec
- Adapted resource clients to renamed/restructured models:
  - `TaskOptions` → `OptionalRunOptions`
  - `ScheduleCreateActions` → discriminated union in `ScheduleCreate`
  - `EnvVar` → `EnvVarRequest` for create/update requests

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Co-authored-by: Vlada Dusek <v.dusek96@gmail.com>