session: update SQLstore to expose db.BaseDB

In preparation for migrating sessions to the new SQLstore, we need to
expose db.BaseDB in the SQLstore. Therefore we change the SQLstore
to embed the BaseDB interface, rather than the concrete *sql.DB type.

Author: ViktorT-11

session/sql_store.go

@@ -65,8 +65,8 @@ type SQLStore struct {
 	// in order to implement all its CRUD logic.
 	db BatchedSQLQueries
 
-	// DB represents the underlying database connection.
-	*sql.DB
+	// BaseDB represents the underlying database connection.
+	*db.BaseDB
 
 	clock clock.Clock
 }
@@ -81,9 +81,9 @@ func NewSQLStore(sqlDB *db.BaseDB, clock clock.Clock) *SQLStore {
 	)
 
 	return &SQLStore{
-		db:    executor,
-		DB:    sqlDB.DB,
-		clock: clock,
+		db:     executor,
+		BaseDB: sqlDB,
+		clock:  clock,
 	}
 }