Migrate from Checker Framework annotations to JSpecify annotations.

This is the next step toward [using JSpecify in Guava](jspecify/jspecify#239 (comment)).

RELNOTES=Migrated from Checker Framework annotations to JSpecify annotations.
PiperOrigin-RevId: 708707163

Author: cpovirk

android/guava-testlib/src/com/google/common/collect/testing/AbstractCollectionTester.java

@@ -20,7 +20,7 @@
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.util.Collection;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.junit.Ignore;
 
 /**

android/guava-testlib/src/com/google/common/collect/testing/AbstractContainerTester.java

@@ -28,7 +28,7 @@
 import java.util.Collection;
 import java.util.List;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.junit.Ignore;
 
 /**

android/guava-testlib/src/com/google/common/collect/testing/AbstractIteratorTester.java

@@ -35,7 +35,7 @@
 import java.util.Set;
 import java.util.Stack;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Most of the logic for {@link IteratorTester} and {@link ListIteratorTester}.

android/guava-testlib/src/com/google/common/collect/testing/AbstractMapTester.java

@@ -27,7 +27,7 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.junit.Ignore;
 
 /**

android/guava-testlib/src/com/google/common/collect/testing/AbstractTester.java

@@ -21,7 +21,7 @@
 import com.google.common.annotations.J2ktIncompatible;
 import junit.framework.TestCase;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * This abstract base class for testers allows the framework to inject needed information after

android/guava-testlib/src/com/google/common/collect/testing/BaseComparable.java

@@ -18,7 +18,7 @@
 
 import com.google.common.annotations.GwtCompatible;
 import java.io.Serializable;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple base class to verify that we handle generics correctly.

android/guava-testlib/src/com/google/common/collect/testing/DerivedCollectionGenerators.java

@@ -34,7 +34,7 @@
 import java.util.SortedMap;
 import java.util.SortedSet;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Derived suite generators, split out of the suite builders so that they are available to GWT.

android/guava-testlib/src/com/google/common/collect/testing/FeatureSpecificTestSuiteBuilder.java

@@ -42,7 +42,7 @@
 import junit.framework.Test;
 import junit.framework.TestCase;
 import junit.framework.TestSuite;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Creates, based on your criteria, a JUnit test suite that exhaustively tests the object generated

android/guava-testlib/src/com/google/common/collect/testing/Helpers.java

@@ -45,7 +45,7 @@
 import java.util.Map.Entry;
 import java.util.Set;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 @GwtCompatible(emulated = true)
 @NullMarked

android/guava-testlib/src/com/google/common/collect/testing/IteratorTester.java

@@ -20,7 +20,7 @@
 import java.util.Collections;
 import java.util.Iterator;
 import org.jspecify.annotations.NullMarked;
-import org.checkerframework.checker.nullness.qual.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A utility for testing an Iterator implementation by comparing its behavior to that of a "known