Add new experimental annotation

This will allow Cover to interrogate LLMs on the annotated elements. The exact behaviour is to be determined (hence putting it in an `experimental` package).

Author: pcrane

src/main/java/com/diffblue/cover/annotations/experimental/InTestsUseLLM.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2025 Diffblue Limited.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package com.diffblue.cover.annotations.experimental;
+
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PACKAGE;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Indicates the annotated element can request assistance from LLMs.
+ *
+ * <p>The specific assistance will depend on: the element, what features Diffblue Cover has
+ * implemented, and any number of other things.
+ *
+ * <p><em>Note:</em> this annotation may change in the future without further warning.
+ */
+@Retention(RUNTIME)
+@Target({PACKAGE, TYPE, METHOD, PARAMETER})
+@Deprecated // Well, not really, but I don't want to encourage the use of this annotation
+public @interface InTestsUseLLM {}