feat(core): improve XML formatting and validation rules

- update `prettify_xml` to strip XML declaration for more flexibility
- prepend XML declaration explicitly in Google Merchant feed generation
- adjust pagination `page_size` max limit to 128 for stricter validation

engine/core/feeds/base.py

@@ -162,7 +162,12 @@ class BaseFeedGenerator(ABC):
 
     @staticmethod
     def prettify_xml(elem: Element) -> str:
-        """Return a pretty-printed XML string for the Element."""
+        """Return a pretty-printed XML string for the Element (without XML declaration)."""
         rough_string = tostring(elem, encoding="unicode")
         reparsed = minidom.parseString(rough_string)
-        return reparsed.toprettyxml(indent="  ", encoding=None)
+        pretty = reparsed.toprettyxml(indent="    ")
+        # Strip the XML declaration added by toprettyxml so callers can add their own
+        lines = pretty.split("\n")
+        if lines and lines[0].startswith("<?xml"):
+            lines = lines[1:]
+        return "\n".join(lines).strip()

engine/core/feeds/google_merchant.py

@@ -117,7 +117,7 @@ class GoogleMerchantFeedGenerator(BaseFeedGenerator):
             item = SubElement(channel, "item")
             self._add_product_to_xml(item, product_data)
 
-        return self.prettify_xml(rss)
+        return '<?xml version="1.0" encoding="UTF-8"?>\n' + self.prettify_xml(rss)
 
     def _add_product_to_xml(self, item: Element, product_data: dict[str, Any]) -> None:
         """Add a product's data to an XML item element."""

schon/pagination.py

@@ -13,7 +13,7 @@ class CustomPagination(PageNumberPagination):
     def get_paginated_response(self, data: list[dict[Any, Any]]) -> Response:
         if not self.page_size:
             self.page_size = 88
-        if not 1 <= self.page_size <= 255:
+        if not 1 <= self.page_size <= 128:
             raise ValueError("Page size must be between 1 and 255")
         if not self.page:
             paginator = Paginator(data, self.page_size)