[Bug]: Missing Closed Generic Query Behavior Registration

[eneshoxha]

Title: Add AddQueryPipelineBehavior<T>() for closed generic query behaviors

Labels: bug, mediator

Body:

Problem

MediatorOptions provides closed-generic registration for commands and notifications:

• AddCommandPipelineBehavior<TBehavior>() -- closed generic
• AddNotificationPipelineBehavior<TBehavior>() -- closed generic

But queries only have:

• AddOpenQueryPipelineBehavior(Type) -- open generic only

There is no AddQueryPipelineBehavior<TBehavior>() for registering a closed generic query behavior (e.g., a behavior that only applies to GetUserQuery).

Proposed Solution

Add the missing method to MediatorOptions:

public MediatorOptions AddQueryPipelineBehavior<TBehavior>()
    where TBehavior : class
{
    var behaviorType = typeof(TBehavior);

    if (behaviorType.IsGenericTypeDefinition)
        throw new ArgumentException("Open generic types must be registered using AddOpenQueryPipelineBehavior");

    var implementsQueryBehavior =
        behaviorType.GetInterfaces().Any(i => i.IsGenericType &&
                                              i.GetGenericTypeDefinition() == typeof(IQueryPipelineBehavior<,>));

    if (!implementsQueryBehavior)
        throw new ArgumentException("Type must implement IQueryPipelineBehavior<,>");

    QueryBehaviors.Add(behaviorType);
    return this;
}

Also update RegisterPipelineBehaviors in ServiceCollectionExtensions.cs to handle closed query behaviors the same way it handles closed notification behaviors (checking IsGenericTypeDefinition and registering against specific interfaces).