replace complicated list comprehensions with some for loops

src/_zkapauthorizer/tests/matchers.py

@@ -135,15 +135,17 @@ def leases_current(relevant_storage_indexes, now, min_lease_remaining):
     servers for which the leases on the given storage indexes do not expire
     before ``min_lease_remaining``.
     """
+    def get_relevant_stats(storage_server):
+        for (storage_index, shares) in storage_server.buckets.items():
+            if storage_index in relevant_storage_indexes:
+                for (sharenum, stat) in shares.items():
+                    yield stat
+
+
     return AfterPreprocessing(
         # Get share stats for storage indexes we should have
         # visited and maintained.
-        lambda storage_server: list(
-            stat
-            for (storage_index, shares) in storage_server.buckets.items()
-            if storage_index in relevant_storage_indexes
-            for (sharenum, stat) in shares.items()
-        ),
+        lambda storage_server: list(get_relevant_stats(storage_server)),
         AllMatch(
             AfterPreprocessing(
                 # Lease expiration for anything visited must be