fix: handle default case in split_pdf when page_ranges is None

The split_pdf method was raising ValueError when page_ranges was None,
but the docstring and tests expect it to default to extracting the
first page. Updated to set page_ranges to [{"start": 0, "end": 1}]
when None is provided.

This fixes the failing test_split_pdf_single_page_default test.

Author: jdrhyne

src/nutrient_dws/api/direct.py

@@ -283,7 +283,8 @@ def split_pdf(
 
         # Validate inputs
         if not page_ranges:
-            raise ValueError("page_ranges is required")
+            # Default behavior: extract first page only
+            page_ranges = [{"start": 0, "end": 1}]
 
         if len(page_ranges) > 50:
             raise ValueError("Maximum 50 page ranges allowed")