feat: integration tests for nestjs generator

feat: integration tests for nestjs generator

Description

We have introduced a standardized integration testing pattern to validate that generated feature flag clients are both compilable and usable within their intended language or framework ecosystems. The NestJS generator currently does not have integration test coverage.

We should add integration tests for the NestJS generator using the structure and methodology described in the CLI's testing documentation.

📄 Relevant Documentation:
Integration Testing Pattern

Tasks

• Scaffold a minimal NestJS test project (e.g., using @nestjs/cli)
• Use the NestJS generator to produce a feature flag client
• Validate that the generated code builds, integrates into a NestJS module, and executes a sample flag evaluation
• Add this test to the integration test suite and ensure it runs in CI
• Update test documentation if any NestJS-specific considerations arise

Acceptance Criteria

• ✅ NestJS generator is covered by at least one integration test
• ✅ Generated NestJS client compiles and integrates into a real app
• ✅ Integration test runs automatically in CI
• ✅ Test conforms to the documented integration testing pattern

Additional Notes

This test will help prevent regressions and ensure confidence that the NestJS generator produces valid, working clients suitable for real-world usage.

Start with test/README.md and the existing integration tests to follow the documented pattern for the NestJS generator. Scaffold the minimal NestJS project, generate the client, verify compilation, module integration, and sample flag evaluation, then confirm the test runs in CI and update documentation if needed.