Seed the retention tests 50 rows per insert, not 500 (closes #198)

Three retention tests made internal/database the slowest test package, mostly by seeding thousands of rows 500 per insert: the SQLite driver finds each parameter's value by scanning the statement's arguments from the first until it reaches that parameter's, so binding grows with the square of the parameter count. They now seed the same rows 50 per insert, about three times faster; no test case or assertion changes. The package drops from 13 to 22s to about 7s. What keeps make test above the 20s target is now mostly the cold -race compile of the tree, which moves with host load. The 90s per-package timeout stays; script/test's header records the new figures.

Model: opus-5-5

internal/database/totals_test.go

@@ -102,6 +102,13 @@ func TestWebhookDBManager_TotalsSurviveReopen(t *testing.T) {
 // seedExpiredEvents stores count events created at the given time,
 // each with a delivered delivery to one target and a failed delivery
 // to the other, and one attempt for each delivery.
+//
+// It and seedBareEvents insert 50 rows per statement, not more. The
+// SQLite driver looks up each parameter's value by scanning the
+// statement's arguments from the first until it reaches that
+// parameter's, so the time to bind a statement grows with the square of
+// its parameter count: at 500 rows, several thousand parameters, the
+// seeding took most of these tests' time under -race.
 func seedExpiredEvents(
 	t *testing.T,
 	db *gorm.DB,
@@ -138,8 +145,8 @@ func seedExpiredEvents(
 		)
 	}
 
-	require.NoError(t, db.CreateInBatches(events, 500).Error)
-	require.NoError(t, db.CreateInBatches(deliveries, 500).Error)
+	require.NoError(t, db.CreateInBatches(events, 50).Error)
+	require.NoError(t, db.CreateInBatches(deliveries, 50).Error)
 
 	results := make([]database.DeliveryResult, len(deliveries))
 	for i := range deliveries {
@@ -148,7 +155,7 @@ func seedExpiredEvents(
 		}
 	}
 
-	require.NoError(t, db.CreateInBatches(results, 500).Error)
+	require.NoError(t, db.CreateInBatches(results, 50).Error)
 }
 
 // seedBareEvents stores count events created at the given time, with
@@ -172,7 +179,7 @@ func seedBareEvents(
 		events[i].CreatedAt = createdAt
 	}
 
-	require.NoError(t, db.CreateInBatches(events, 500).Error)
+	require.NoError(t, db.CreateInBatches(events, 50).Error)
 }
 
 // TestRetentionReaper_PrunesMoreThanOneBatch verifies that a prune