Fix normalize_to_records function which did not traverse into nested elements within a time_series entry

Until now I did not discover nested elements within a time_series entry but the ProductionAndGenerationUnits endpoint returns those.
This change may increase the number of rows and columns for existing queries but its absolutely necessary for not silently dropping data.
Endpoints like Load and EnergyPrices are not affected as they do not have nested structures in the `time_series` objects.

Author: BerriJ

src/entsoe/utils/records.py

@@ -69,14 +69,18 @@ def _filter_ignored_fields(record: Dict[str, Any]) -> Dict[str, Any]:
         return {k: v for k, v in record.items() if k not in ignore_fields}
 
     if isinstance(data, dict):
-        items = {}
+        items: Dict[str, Any] = {}
+        expansions: List[List[Dict[str, Any]]] = []
         for k, v in data.items():
             new_key = f"{parent_key}{sep}{k}" if parent_key else k
             if isinstance(v, dict):
                 sub_records = normalize_to_records(
                     v, new_key, sep=sep, ignore_fields=ignore_fields
                 )
-                items.update(sub_records[0])  # merge dict
+                if len(sub_records) == 1:
+                    items.update(sub_records[0])
+                elif len(sub_records) > 1:
+                    expansions.append(sub_records)
             elif isinstance(v, list):
                 # Expand list elements into multiple records
                 list_records = []
@@ -88,14 +92,15 @@ def _filter_ignored_fields(record: Dict[str, Any]) -> Dict[str, Any]:
                         list_records.extend(sub_records)
                     else:
                         list_records.append({new_key: elem})
-                # Cross join if multiple records, else just keep one
                 if list_records:
-                    return [
-                        _filter_ignored_fields(dict(items, **lr)) for lr in list_records
-                    ]
+                    expansions.append(list_records)
             else:
                 items[new_key] = v
-        return [_filter_ignored_fields(items)]
+        # Cross-join base items with all collected expansions
+        result: List[Dict[str, Any]] = [items]
+        for expansion in expansions:
+            result = [dict(r, **e) for r in result for e in expansion]
+        return [_filter_ignored_fields(r) for r in result]
     elif isinstance(data, list):
         records = []
         for elem in data: