Fix ConcurrentModificationException in DeclarativeRecipe

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Summary

• DeclarativeRecipe.recipeList and preconditions are mutable ArrayList fields that are populated during initialize() (via clear() + add()) and concurrently iterated by getDataTableDescriptors(), createRecipeDescriptor(), and getRecipeList()
• Under concurrent access from virtual threads calling describe()/getDescriptor() on the same recipe instance, this causes ConcurrentModificationException
• Fix: make both fields volatile and assign immutable list snapshots from initialize(). Readers always see a complete, immutable list — no CME possible, and no risk of duplicate entries from interleaved initialize() calls

Why not align with Recipe.getRecipeList() (fresh list per call)?

The base Recipe.getRecipeList() builds a new list every call via buildRecipeList() — inherently thread-safe, no shared state. We considered making DeclarativeRecipe follow this pattern, but it isn't feasible: DeclarativeRecipe resolves LazyLoadedRecipe references by name during initialize(), which requires the availableRecipes context that is only available at startup. The recipe list is data-driven (YAML), not code-driven, so it must be built once and cached. The volatile + immutable swap gives the same thread-safety guarantees while preserving this lifecycle.

Changes

• recipeList and preconditions declared as volatile, initialized to Collections.emptyList()
• initialize(List, List, Function, Set) refactored to initialize(List, Function, Set) — builds a new ArrayList internally, returns Collections.unmodifiableList(result)
• Callers assign the returned list directly: recipeList = initialize(...)
• No changes needed to iteration sites — they now iterate immutable snapshots

Test plan

• Added getDataTableDescriptorsThreadSafe — concurrent reader/writer threads that reproduces the CME
• Added concurrentInitializeDoesNotDuplicateRecipes — concurrent initialize() calls don't produce duplicate entries
• Verified both tests fail without the fix, pass with it
• All existing DeclarativeRecipeTest tests pass