packagist: Yield pages of origins to regularly record origins

Instead of sending one page with all origins listed which is britle.
When something goes wrong during the listing, the lister currently records nothing.

swh/lister/packagist/lister.py

@@ -13,6 +13,7 @@ import iso8601
 import requests
 from tenacity import RetryError
 
+from swh.core.utils import grouper
 from swh.scheduler.interface import SchedulerInterface
 from swh.scheduler.model import ListedOrigin
 
@@ -126,12 +127,11 @@ class PackagistLister(Lister[PackagistListerState, PackagistPageType]):
             return {}
 
     def get_pages(self) -> Iterator[PackagistPageType]:
-        """
-        Yield a single page listing all Packagist projects (randomly).
-        """
+        """Retrieve & randomize unique list of packages into pages of packages."""
         package_names = self.api_request(self.url)["packageNames"]
         shuffle(package_names)
-        yield package_names
+        for page_packages in grouper(package_names, n=self.record_batch_size):
+            yield page_packages
 
     def _get_metadata_from_page(
         self, package_url_format: str, package_name: str

swh/lister/pattern.py

@@ -356,6 +356,7 @@ class Lister(Generic[StateType, PageType]):
                 else:
                     logger.warning("Skipping invalid origin: %s", origin.url)
 
+            logger.debug("Record valid %s origins in the scheduler", len(valid_origins))
             ret = self.scheduler.record_listed_origins(valid_origins)
             recorded_origins.extend(origin.url for origin in ret)