change: Create core registry infrastructure

[mathysgrapotte]

Is your change request related to a problem? Please describe.

Need shared foundation for component registries to avoid code duplication.

Describe the solution you'd like

1. Create src/stimulus/core/registry.py with:
   • BaseRegistry class handling entry points/decorators
   • Generic type enforcement for components
   • Plugin loading system
2. Add basic tests for registration/instantiation
3. Document base class usage for developers

Describe alternatives you've considered

Additional context

Required for all component registries. Example usage:

class ComponentRegistry(BaseRegistry[AbstractComponent]):

[mathysgrapotte]

could be something like this :

"""Central registry system for Stimulus components."""
from importlib.metadata import entry_points
from typing import Type, Dict, TypeVar, Generic

T = TypeVar('T')

class BaseRegistry(Generic[T]):
    """Base registry class for component registration."""
    
    def __init__(self, entry_point_group: str, base_class: Type[T]):
        self._components: Dict[str, Type[T]] = {}
        self.entry_point_group = entry_point_group
        self.base_class = base_class
        self.load_builtins()
        self.load_plugins()

    def register(self, name: str) -> callable:
        """Decorator factory for component registration."""
        def decorator(cls: Type[T]):
            if not issubclass(cls, self.base_class):
                raise TypeError(f"{cls.__name__} must subclass {self.base_class.__name__}")
            self._components[name] = cls
            return cls
        return decorator

    def load_builtins(self):
        """Override in child classes to register built-in components"""
        pass

    def load_plugins(self):
        """Load external components from entry points"""
        for ep in entry_points().select(group=self.entry_point_group):
            self._components[ep.name] = ep.load()

    def get(self, name: str, **params) -> T:
        """Instantiate a component with parameters"""
        cls = self._components.get(name)
        if not cls:
            available = ", ".join(self._components.keys())
            raise ValueError(f"Unknown {self.base_class.__name__} '{name}'. Available: {available}")
        return cls(**params)

    @property
    def component_names(self):
        return list(self._components.keys())