feat(dotnet): leverage OpenFeature.DependencyInjection package for improved code generation

Summary

Enhance the .NET code generator to leverage the latest improvements from openfeature/dotnet-sdk, specifically using OpenFeature.DependencyInjection or OpenFeature.Hosting packages to generate code that better aligns with modern .NET dependency injection patterns and the SDK's recommended practices.

Motivation

The current generated code doesn't fully embrace the DI-first philosophy of the underlying OpenFeature SDK. By utilizing the official DI packages, we can:

• Generate code that follows .NET best practices and conventions
• Provide better integration with ASP.NET Core and other .NET hosting scenarios
• Reduce boilerplate and improve developer experience
• Ensure generated code stays aligned with SDK evolution and recommendations

Proposed Solution

Update the dotnet generator to:

1. Include OpenFeature.DependencyInjection or OpenFeature.Hosting package references in generated projects
2. Generate service registration code using OpenFeature.DependencyInjection or OpenFeature.Hosting with extension methods

Related Issues

• Builds upon #208 which provides a quick-fix for DI issues using .NET Standard as a first step
• This issue represents the longer-term, more comprehensive solution

Start with the .NET generator and the generated project output, then review #208 and the current OpenFeature.DependencyInjection and OpenFeature.Hosting recommendations. Compare the package-reference and service-registration alternatives described here. Done means generated projects use the selected official package and extension-method registration pattern while addressing the DI concerns in #208.