misc: catch json_encode exception to help identifying parsing errors

This brings two improvements:

- The reason for the JSON parsing failure is visible in the stack
  trace / `$previous` exception, allowing the developer to determine
  whether the parsing failure was caused by a syntax error, invalid
  UTF-8 sequence or something else.
- The JSON string null (which decodes to null) is no longer erroneously
  rejected as invalid. Instead it is rejected, because it is not
  iterable, slightly improving the error reporting.

rector.php

@@ -36,9 +36,6 @@
         UnionTypesRector::class => [
             __DIR__ . '/tests/Unit/Definition/Repository/Reflection/ReflectionClassDefinitionRepositoryTest',
         ],
-        JsonThrowOnErrorRector::class => [
-            __DIR__ . '/src/Mapper/Source/JsonSource.php',
-        ],
         MixedTypeRector::class => [
             __DIR__ . '/tests/Integration/Mapping/Object/UnionValuesMappingTest.php',
             __DIR__ . '/tests/Unit/Definition/Repository/Reflection/ReflectionClassDefinitionRepositoryTest',

src/Mapper/Source/Exception/InvalidJson.php

@@ -4,16 +4,18 @@
 
 namespace CuyZ\Valinor\Mapper\Source\Exception;
 
+use JsonException;
 use RuntimeException;
 
 /** @internal */
 final class InvalidJson extends RuntimeException implements InvalidSource
 {
-    public function __construct(private string $source)
+    public function __construct(private string $source, ?JsonException $previous = null)
     {
         parent::__construct(
             'Invalid JSON source.',
-            1566307185
+            1566307185,
+            $previous
         );
     }
 

src/Mapper/Source/JsonSource.php

@@ -9,11 +9,14 @@
 use CuyZ\Valinor\Mapper\Source\Exception\SourceNotIterable;
 use Iterator;
 use IteratorAggregate;
+use JsonException;
 use Traversable;
 
 use function is_iterable;
 use function json_decode;
 
+use const JSON_THROW_ON_ERROR;
+
 /**
  * @api
  *
@@ -29,10 +32,10 @@ final class JsonSource implements IteratorAggregate
      */
     public function __construct(string $jsonSource)
     {
-        $source = json_decode($jsonSource, true);
-
-        if ($source === null) {
-            throw new InvalidJson($jsonSource);
+        try {
+            $source = json_decode($jsonSource, associative: true, flags: JSON_THROW_ON_ERROR);
+        } catch (JsonException $e) {
+            throw new InvalidJson($jsonSource, $e);
         }
 
         if (! is_iterable($source)) {