feat(abstractions): add ILambdaMiddlewareFactory interface

[j-d-ha]

Description

Add an ILambdaMiddlewareFactory interface to support custom middleware creation logic.

Motivation

Currently, middleware can be registered using UseMiddleware<T>(), but there's no built-in way to customize how middleware instances are created. A factory interface would enable:

• Custom middleware initialization logic
• Advanced dependency injection scenarios
• Middleware pooling or reuse strategies
• Complex constructor parameter resolution

Proposed Interface

public interface ILambdaMiddlewareFactory
{
    ILambdaMiddleware Create(Type middlewareType);
}

Or with generics:

public interface ILambdaMiddlewareFactory
{
    TMiddleware Create<TMiddleware>() where TMiddleware : ILambdaMiddleware;
}

Implementation Considerations

• Should integrate with the existing middleware pipeline
• Should work seamlessly with UseMiddleware<T>()
• Consider whether to support both generic and non-generic versions
• Determine whether factory should be registered per middleware type or globally
• Consider lifetime management (transient, scoped, singleton)

Acceptance Criteria

• ILambdaMiddlewareFactory interface is added to MinimalLambda.Abstractions
• Factory can be registered with the host builder
• Factory is used when creating middleware instances
• Unit tests cover factory integration
• Example demonstrates custom factory usage
• Documentation explains when and how to use the factory

Related

This relates to the existing class-based middleware support introduced in #257.