feat: add support for JSON_FORCE_OBJECT option in JSON normalizer

```php
(new \CuyZ\Valinor\MapperBuilder())
    ->normalizer(Format::json())
    ->withOptions(JSON_FORCE_OBJECT)
    ->normalize(['foo', 'bar']);

// {"0":"foo","1":"bar"}
```

src/Normalizer/Formatter/JsonFormatter.php

@@ -17,6 +17,7 @@
 use function is_scalar;
 use function json_encode;
 
+use const JSON_FORCE_OBJECT;
 use const JSON_THROW_ON_ERROR;
 
 /** @internal */
@@ -54,8 +55,11 @@ public function format(mixed $value): void
             // afterward, this leads to a JSON array being written, while it
             // should have been an object. This is a trade-off we accept,
             // considering most generators starting at 0 are actually lists.
-            $isList = ($value instanceof Generator && $value->key() === 0)
-                || (is_array($value) && array_is_list($value));
+            $isList = ! ($this->jsonEncodingOptions & JSON_FORCE_OBJECT)
+                && (
+                    ($value instanceof Generator && $value->key() === 0)
+                    || (is_array($value) && array_is_list($value))
+                );
 
             $isFirst = true;
 

src/Normalizer/JsonNormalizer.php

@@ -14,6 +14,7 @@
 use function is_resource;
 use function stream_get_contents;
 
+use const JSON_FORCE_OBJECT;
 use const JSON_HEX_AMP;
 use const JSON_HEX_APOS;
 use const JSON_HEX_QUOT;
@@ -34,7 +35,8 @@
  */
 final class JsonNormalizer implements Normalizer
 {
-    private const ACCEPTABLE_JSON_OPTIONS = JSON_HEX_QUOT
+    private const ACCEPTABLE_JSON_OPTIONS = JSON_FORCE_OBJECT
+    | JSON_HEX_QUOT
     | JSON_HEX_TAG
     | JSON_HEX_AMP
     | JSON_HEX_APOS

tests/Integration/Normalizer/NormalizerTest.php

@@ -30,6 +30,7 @@
 
 use function array_merge;
 
+use const JSON_FORCE_OBJECT;
 use const JSON_HEX_TAG;
 use const JSON_THROW_ON_ERROR;
 
@@ -194,6 +195,21 @@ public static function normalize_basic_values_yields_expected_output_data_provid
             'expected json' => '{"foo":"foo","bar":"bar"}',
         ];
 
+        yield 'list' => [
+            'input' => ['foo', 'bar'],
+            'expected array' => ['foo', 'bar'],
+            'expected json' => '["foo","bar"]',
+        ];
+
+        yield 'list kept as object in json' => [
+            'input' => ['foo', 'bar'],
+            'expected array' => ['foo', 'bar'],
+            'expected json' => '{"0":"foo","1":"bar"}',
+            [],
+            [],
+            JSON_FORCE_OBJECT
+        ];
+
         yield 'ArrayObject' => [
             'input' => new ArrayObject(['foo' => 'foo', 'bar' => 'bar']),
             'expected array' => [
@@ -1148,16 +1164,13 @@ public function test_json_transformer_will_always_throw_on_error(): void
 
     public function test_json_transformer_only_accepts_acceptable_json_options(): void
     {
-        $normalizer = $this->mapperBuilder()->normalizer(Format::json())->withOptions(JSON_FORCE_OBJECT);
-        self::assertSame(JSON_THROW_ON_ERROR, (fn () => $this->jsonEncodingOptions)->call($normalizer));
-
         $normalizer = $this->mapperBuilder()->normalizer(Format::json())->withOptions(JSON_PARTIAL_OUTPUT_ON_ERROR);
         self::assertSame(JSON_THROW_ON_ERROR, (fn () => $this->jsonEncodingOptions)->call($normalizer));
 
         $normalizer = $this->mapperBuilder()->normalizer(Format::json())->withOptions(JSON_PRETTY_PRINT);
         self::assertSame(JSON_THROW_ON_ERROR, (fn () => $this->jsonEncodingOptions)->call($normalizer));
 
-        $normalizer = $this->mapperBuilder()->normalizer(Format::json())->withOptions(JSON_FORCE_OBJECT | JSON_PARTIAL_OUTPUT_ON_ERROR | JSON_PRETTY_PRINT);
+        $normalizer = $this->mapperBuilder()->normalizer(Format::json())->withOptions(JSON_PARTIAL_OUTPUT_ON_ERROR | JSON_PRETTY_PRINT);
         self::assertSame(JSON_THROW_ON_ERROR, (fn () => $this->jsonEncodingOptions)->call($normalizer));
     }
 }