refactor: render fragment explicitly

Instead of including the template for non-hx-requests, inject the
rendered fragment.

templates/index.html

@@ -6,14 +6,16 @@
         <p>A new old way to build web applications</p>
     </hgroup>
     <table>
-    {% if users.is_some() %}
-        {% include "fragment/user/table.html" %}
-    {% else %}
-        <tr><td>
-            <button hx-get="/user" hx-target="table" hx-push-url="true">
-                Load data
-            </button>
-        </td></tr>
-    {% endif %}
+
+    {% match fragment %}
+        {% when Some with (fragment) %}
+            {{ fragment|safe }}
+        {% when None %}
+            <tr><td>
+                <button hx-get="/user" hx-target="table" hx-push-url="true">
+                    Load data
+                </button>
+            </td></tr>
+    {% endmatch %}
     </table>
 {% endblock %}