Generic constructor

Creates a Generic annotation instance.

Parameters:

• _type: The base generic type (e.g., List for List<T>)
• _uri: Optional source URI for better debugging

Throws:

• InvalidArgumentException if _type represents a non-generic type

Example:

@Generic(DataPipe, 'dart:async')
class DataPipe<T> {
  Stream<T> get stream => _controller.stream;
}