synchronize access to IdentityHashMap instances

... to avoid concurrency issues like in build https://github.com/datafaker-net/datafaker/actions/runs/23618303854/job/68791305528?pr=1785:

```
java.lang.ClassCastException: class net.datafaker.providers.base.Color cannot be cast to class net.datafaker.providers.base.Vehicle (net.datafaker.providers.base.Color and net.datafaker.providers.base.Vehicle are in unnamed module of loader 'app')
	at net.datafaker.providers.base.BaseProviders.vehicle(BaseProviders.java:506)
	at net.datafaker.providers.base.VehicleLocaleTest.lambda$localeProviderListTest$3(VehicleLocaleTest.java:23)
```

Class `IdentityHashMap` is not thread-safe, all accesses to this class should be synchronized.

Author: asolntsev

src/main/java/net/datafaker/providers/base/BaseFaker.java

@@ -22,6 +22,8 @@
 import java.util.function.Predicate;
 import java.util.function.Supplier;
 
+import static java.util.Collections.synchronizedMap;
+
 /**
  * Provides utility methods for generating fake strings, such as names, phone
  * numbers, addresses. generate random strings with given patterns
@@ -32,7 +34,7 @@ public class BaseFaker implements BaseProviders {
     private static final Predicate<Class<?>> EVERY_PROVIDER_ALLOWED = t -> true;
     private final FakerContext context;
     private final FakeValuesService fakeValuesService;
-    private final Map<Class<?>, AbstractProvider<?>> providersCache = new IdentityHashMap<>();
+    private final Map<Class<?>, AbstractProvider<?>> providersCache = synchronizedMap(new IdentityHashMap<>());
     private final Predicate<Class<?>> whiteListPredicate;
 
     public BaseFaker() {

src/main/java/net/datafaker/providers/base/ObjectMethods.java

@@ -7,11 +7,12 @@
 import java.util.Set;
 import java.util.stream.Stream;
 
+import static java.util.Collections.synchronizedMap;
 import static java.util.stream.Collectors.toMap;
 
 public class ObjectMethods {
-    private static final Map<Class<?>, Map<String, Method>> METHODS_BY_NAME = new IdentityHashMap<>();
-    private static final Map<Class<?>, Map<String, Method>> METHODS_BY_RETURN_TYPE = new IdentityHashMap<>();
+    private static final Map<Class<?>, Map<String, Method>> METHODS_BY_NAME = synchronizedMap(new IdentityHashMap<>());
+    private static final Map<Class<?>, Map<String, Method>> METHODS_BY_RETURN_TYPE = synchronizedMap(new IdentityHashMap<>());
     private static final Set<String> IGNORED_METHODS = Set.of("equals", "hashCode", "toString", "Builder", "stream");
 
     private static synchronized Map<String, Method> scanMethodsByName(Class<?> clazz) {

src/main/java/net/datafaker/service/FakerContext.java

@@ -20,7 +20,7 @@ public class FakerContext {
     private static final Pattern LOCALE = Pattern.compile("[-_]");
     private static final Map<SingletonLocale, List<SingletonLocale>> LOCALE_2_LOCALES_CHAIN = new IdentityHashMap<>();
     private static final Map<SingletonLocale, SingletonLocale> STRING_LOCALE_HASH_MAP = new IdentityHashMap<>();
-    public static final List<SingletonLocale> DEFAULT_SINGLETON_LOCALE_LIST = List.of(DEFAULT_LOCALE);
+    private static final List<SingletonLocale> DEFAULT_SINGLETON_LOCALE_LIST = List.of(DEFAULT_LOCALE);
     private static final Map<String, String> LANGUAGE_DEFAULT_COUNTRY = Map.ofEntries(
         Map.entry("be", "BY"),
         Map.entry("cs", "CZ"),

src/main/java/net/datafaker/transformations/JavaObjectTransformer.java

@@ -18,9 +18,11 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import static java.util.Collections.synchronizedMap;
+
 public class JavaObjectTransformer implements Transformer<Object, Object> {
-    private static final Map<Schema<Object, ?>, Consumer<Object>> SCHEMA2CONSUMER = new IdentityHashMap<>();
-    private static final Map<Class<?>, Constructor<?>> CLASS2CONSTRUCTOR = new IdentityHashMap<>();
+    private static final Map<Schema<Object, ?>, Consumer<Object>> SCHEMA2CONSUMER = synchronizedMap(new IdentityHashMap<>());
+    private static final Map<Class<?>, Constructor<?>> CLASS2CONSTRUCTOR = synchronizedMap(new IdentityHashMap<>());
 
     private Optional<Object> sourceClazz = Optional.empty();