feat: middleware V2

[xavidop]

Description

Re-design middleware to implement a v2 to wrap, generate, models and tools

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• CI/CD improvements

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• All existing tests pass

Checklist

• My code follows the project's code style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Documentation

• README updated
• Plugin documentation updated
• API documentation updated
• Sample code updated

[gemini-code-assist]

Code Review

This pull request introduces the V2 GenerationMiddleware system, which provides granular hooks for the generation pipeline (Generate, Model, and Tool). It includes the core interfaces, parameter objects, and a base implementation, along with comprehensive tests and a new sample project. The Genkit class has been updated to support these hooks during generation, and a new ReflectionServerV2 has been implemented using WebSockets and JSON-RPC 2.0 for improved dev tool integration. Review feedback identified a critical bug in the action cancellation logic where all actions were interrupted regardless of trace ID, a missing implementation for streaming in the reflection server, and a failure to collect tools provided by middleware.