Only add scalar meta data to image dataset

Prevents attributes containing arrays or maps from breaking rendering
with an "array to string" conversion error, see xp-forge/handlebars#24

This will permit us to refactor meta data more freely in the future,
e.g. as see in the "Extract colors" pull request, #36

Author: thekid

src/main/handlebars/partials/images.handlebars

@@ -7,7 +7,7 @@
         </video>
       {{else}}
         <a href="/image/{{in.slug}}/full-{{name}}.webp" data-lightbox>
-          <img alt="{{title}}, {{date meta.dateTime format='d.m.Y H:i'}}" {{#unless first}}loading="lazy"{{/unless}} {{#each meta}}data-{{@key}}="{{.}}"{{/each}} src="/image/{{in.slug}}/thumb-{{name}}.webp" width="1024">
+          <img alt="{{title}}, {{date meta.dateTime format='d.m.Y H:i'}}" {{#unless first}}loading="lazy"{{/unless}} {{&dataset meta}} src="/image/{{in.slug}}/thumb-{{name}}.webp" width="1024">
         </a>
       {{/if}}
     </div>

src/main/php/de/thekid/dialog/Helpers.php

@@ -7,6 +7,7 @@
  *
  * - range <from> <until>
  * - route <entry>
+ * - dataset <meta-inf>
  *
  * @test  de.thekid.dialog.unittest.HelpersTest
  */ 
@@ -29,5 +30,12 @@ public function helpers() {
         return 'content/'.$entry['slug'];
       }
     };
+    yield 'dataset' => function($node, $context, $options) {
+      $r= '';
+      foreach ($options[0] as $key => $value) {
+        is_scalar($value) && $r.= ' data-'.htmlspecialchars($key).'="'.htmlspecialchars($value).'"';
+      }
+      return $r;
+    };
   }
 }

src/test/php/de/thekid/dialog/unittest/HelpersTest.php

@@ -24,4 +24,20 @@ public function range($options, $expected) {
   public function route($entry, $expected) {
     Assert::equals($expected, $this->helpers['route'](null, null, [$entry]));
   }
+
+  #[Test]
+  public function dataset() {
+    Assert::equals(
+      ' data-string="value" data-yes="1" data-no="" data-number="2022"',
+      $this->helpers['dataset'](null, null, [[
+        'string' => 'value',
+        'yes'    => true,
+        'no'     => false,
+        'number' => 2022,
+        'array'  => ['ignored'],
+        'map'    => ['also' => 'ignored'],
+        'nulls'  => null,
+      ]])
+    );
+  }
 }