Make DeclarativeRecipe.accumulator thread-safe with ThreadLocal

DeclarativeRecipe.accumulator was a plain field that gets set during the
scan phase via getInitialValue(). When the same DeclarativeRecipe instance
is shared across concurrent recipe runs (e.g. via a recipe cache), one
run's scan phase overwrites the accumulator set by another run. This
causes the second run to use stale or null accumulator state during the
edit phase, resulting in precondition scanning recipes producing incorrect
results (typically 0 file changes).

This changes the accumulator field to a ThreadLocal so each run thread
gets its own independent accumulator. The clone() method is also
overridden to create a fresh ThreadLocal for cloned instances.

Author: kmccarp

rewrite-core/src/main/java/org/openrewrite/config/DeclarativeRecipe.java

@@ -161,17 +161,16 @@ private void initializeDeclarativeRecipe(DeclarativeRecipe declarativeRecipe, St
         }
     }
 
-    @SuppressWarnings("NotNullFieldNotInitialized")
     @JsonIgnore
-    private transient Accumulator accumulator;
+    private transient ThreadLocal<Accumulator> accumulator = new ThreadLocal<>();
 
     @Override
     public Accumulator getInitialValue(ExecutionContext ctx) {
         Accumulator acc = new Accumulator();
         for (Recipe precondition : preconditions) {
             registerNestedScanningRecipes(precondition, acc, ctx);
         }
-        accumulator = acc;
+        accumulator.set(acc);
         return acc;
     }
 
@@ -509,7 +508,8 @@ private TreeVisitor<?, ExecutionContext> orVisitors(Recipe recipe) {
             //noinspection rawtypes
             ScanningRecipe scanning = (ScanningRecipe) recipe;
             //noinspection unchecked
-            conditions.add(scanning.getVisitor(accumulator.recipeToAccumulator.get(scanning)));
+            Accumulator acc = accumulator.get();
+            conditions.add(scanning.getVisitor(acc != null ? acc.recipeToAccumulator.get(scanning) : null));
         } else {
             conditions.add(recipe.getVisitor());
         }
@@ -602,6 +602,13 @@ private static class LazyLoadedRecipe extends Recipe {
         String description = "Recipe that is loaded lazily.";
     }
 
+    @Override
+    public DeclarativeRecipe clone() {
+        DeclarativeRecipe cloned = (DeclarativeRecipe) super.clone();
+        cloned.accumulator = new ThreadLocal<>();
+        return cloned;
+    }
+
     @Override
     protected RecipeDescriptor createRecipeDescriptor() {
         List<RecipeDescriptor> preconditionDescriptors = new ArrayList<>();