Fix NPE when a workflow implementation uses a composed @WorkflowImpl annotation

[muhrifqii]

What was changed

WorkersTemplate#configureWorkflowImplementationsByWorkerName now uses AnnotationUtils.findAnnotation instead of Class#getAnnotation to look up @WorkflowImpl.
Added AutoDiscoveryComposedAnnotationTest and a dedicated composedannotation fixture package that reproduce the bug with a user-defined composed annotation on both a workflow and an activity implementation.

Why?

If a workflow implementation class is annotated with a custom composed (meta) annotation, for example a user-defined annotation that is itself annotated with @WorkflowImpl, rather than @WorkflowImpl applied directly - worker auto-discovery threw an NPE.
Class#getAnnotation only resolves annotations present directly on the class, so it returned null, and the next line (annotation.workers()) NPE'd.

@ActivityImpl/@NexusServiceImpl lookups were already consistent throughout, which is why only workflows registered via workers() were affected.

Checklist

1. Closes N/A - found while implementing temporal-spring-boot-autoconfigure in an application with a custom composed annotation.

2. How was this tested:
   Added AutoDiscoveryComposedAnnotationTest, confirmed it reproduces the NPE before the fix and passes after
   Ran the full temporal-spring-boot-autoconfigure test suite; all tests pass.

3. Any docs updates needed?
   No.

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