feat: add lazy loading for feature cases

[danielfbm]

This adds a new LazyFeatureCaseBuilder type that allows lazily loading feature cases only when needed. This avoids creating all feature cases upfront when defining the module.

A new GetFeatureCase method on moduleCase allows retrieving a lazy feature case builder by name.

The FeatureCaseBuilder interface is introduced with Labels() to get labels on feature cases. lazyFeatureCaseBuilder implements this to look up the real feature case labels only when Labels() is called.

additionalAssertions on testPoint now accepts FeatureCaseBuilder instead of *featureCase directly.

before the change:

after:

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