Support gRPC via wrapper package

## Feature request

Add gRPC support to NextRush as a **wrapper package** instead of building a custom gRPC implementation from scratch.

### Motivation

NextRush already has a strong transport-agnostic architecture. gRPC should fit as an additional transport layer for service-to-service communication, while keeping the core framework clean and focused.

### Proposal

Create a dedicated wrapper package, for example:

- `@nextrush/grpc`

This package can integrate existing gRPC tooling and expose a clean NextRush-friendly API without reinventing the protocol stack.

### Why a wrapper package

- Avoid duplicating proven gRPC internals
- Keep NextRush core lightweight and transport-agnostic
- Make adoption easier for users who already know gRPC
- Reduce maintenance burden by relying on established libraries

### Expected capabilities

- Load and register `.proto` service definitions
- Map gRPC handlers into NextRush style application code
- Support unary and streaming RPCs
- Handle metadata, status codes, and errors
- Work alongside existing HTTP adapters without forcing a separate framework design

### Notes

The goal is not to build a new gRPC ecosystem inside NextRush. The goal is to provide a polished integration layer that lets users plug gRPC into the framework cleanly.

If this sounds aligned, I can also draft a more concrete API shape for the wrapper package.