Fix extension class visibility to address Kotlin compilation warnings

extensions/src/main/java/dev/cel/extensions/CelComprehensionsExtensions.java

@@ -41,7 +41,7 @@
 import java.util.Optional;
 
 /** Internal implementation of CEL two variable comprehensions extensions. */
-final class CelComprehensionsExtensions
+public final class CelComprehensionsExtensions
     implements CelCompilerLibrary, CelInternalRuntimeLibrary, CelExtensionLibrary.FeatureSet {
 
   private static final String MAP_INSERT_FUNCTION = "cel.@mapInsert";

extensions/src/main/java/dev/cel/extensions/CelListsExtensions.java

@@ -51,9 +51,10 @@
 import java.util.Set;
 
 /** Internal implementation of CEL lists extensions. */
-final class CelListsExtensions
+public final class CelListsExtensions
     implements CelCompilerLibrary, CelInternalRuntimeLibrary, CelExtensionLibrary.FeatureSet {
 
+  /** Supported functions for Lists extension library. */
   @SuppressWarnings({"unchecked"}) // Unchecked: Type-checker guarantees casting safety.
   public enum Function {
     // Note! Creating dependencies on the outer class may cause circular initialization issues.

extensions/src/main/java/dev/cel/extensions/CelMathExtensions.java

@@ -57,7 +57,7 @@
  */
 @SuppressWarnings({"rawtypes", "unchecked"}) // Use of raw Comparables.
 @Immutable
-final class CelMathExtensions
+public final class CelMathExtensions
     implements CelCompilerLibrary, CelRuntimeLibrary, CelExtensionLibrary.FeatureSet {
 
   private static final String MATH_NAMESPACE = "math";

extensions/src/main/java/dev/cel/extensions/CelProtoExtensions.java

@@ -31,7 +31,8 @@
 
 /** Internal implementation of CEL proto extensions. */
 @Immutable
-final class CelProtoExtensions implements CelCompilerLibrary, CelExtensionLibrary.FeatureSet {
+public final class CelProtoExtensions
+    implements CelCompilerLibrary, CelExtensionLibrary.FeatureSet {
 
   private static final String PROTO_NAMESPACE = "proto";
   private static final CelExpr ERROR = CelExpr.newBuilder().setConstant(Constants.ERROR).build();
@@ -148,4 +149,6 @@ private static boolean isTargetInNamespace(CelExpr target) {
     return target.exprKind().getKind().equals(CelExpr.ExprKind.Kind.IDENT)
         && target.ident().name().equals(PROTO_NAMESPACE);
   }
+
+  CelProtoExtensions() {}
 }

extensions/src/main/java/dev/cel/extensions/CelRegexExtensions.java

@@ -37,7 +37,7 @@
 
 /** Internal implementation of CEL regex extensions. */
 @Immutable
-final class CelRegexExtensions
+public final class CelRegexExtensions
     implements CelCompilerLibrary, CelRuntimeLibrary, CelExtensionLibrary.FeatureSet {
 
   private static final String REGEX_REPLACE_FUNCTION = "regex.replace";

extensions/src/main/java/dev/cel/extensions/CelSetsExtensions.java

@@ -41,7 +41,7 @@
  * rewrite the AST into a map to achieve a O(1) lookup.
  */
 @Immutable
-final class CelSetsExtensions
+public final class CelSetsExtensions
     implements CelCompilerLibrary, CelRuntimeLibrary, CelExtensionLibrary.FeatureSet {
 
   private static final String SET_CONTAINS_OVERLOAD_DOC =