Add Effect v4 schema and HttpApiClient plugins

[nmnmcc]

🎯 Changes

• add @kubb/plugin-effect for generating Effect v4 beta schemas from OpenAPI models
• represent OpenAPI date-time values with Effect DateTime.Utc and JSON int64 values with a number-to-bigint codec
• add @kubb/plugin-effect-httpapiclient for generating typed HttpApi, endpoint groups, clients, parameter serialization, cookies, and security layers
• add runnable examples and regression coverage for nested references, date-time annotations, JSON int64 codecs, default responses, and security middleware

The two plugins are kept separate so schema generation can be used independently while the HttpApiClient plugin composes the generated Effect schemas into an Effect HTTP API client.

Related documentation Draft PR: kubb-labs/docs#145

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm run test.

Additional verification:

• pnpm --filter @kubb/plugin-effect test
• pnpm --filter @kubb/plugin-effect typecheck
• pnpm --filter @kubb/plugin-effect build
• pnpm --filter @kubb/plugin-effect-httpapiclient test
• pnpm --filter @kubb/plugin-effect-httpapiclient typecheck
• pnpm --filter @kubb/plugin-effect-httpapiclient build
• pnpm format
• pnpm lint:fix

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is for the docs (no release).

This PR is intentionally a draft pending maintainer review.

[nmnmcc]

Superseded by the Draft PR against the upstream repository: kubb-labs#696