Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

storage/storage.go

@@ -1,44 +0,0 @@
-// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
-// SPDX-License-Identifier: Apache-2.0
-
-package storage // import "miniflux.app/v2/storage"
-
-import (
-	"context"
-	"database/sql"
-	"time"
-)
-
-// Storage handles all operations related to the database.
-type Storage struct {
-	db *sql.DB
-}
-
-// NewStorage returns a new Storage.
-func NewStorage(db *sql.DB) *Storage {
-	return &Storage{db}
-}
-
-// DatabaseVersion returns the version of the database which is in use.
-func (s *Storage) DatabaseVersion() string {
-	var dbVersion string
-	err := s.db.QueryRow(`SELECT current_setting('server_version')`).Scan(&dbVersion)
-	if err != nil {
-		return err.Error()
-	}
-
-	return dbVersion
-}
-
-// Ping checks if the database connection works.
-func (s *Storage) Ping() error {
-	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
-	defer cancel()
-
-	return s.db.PingContext(ctx)
-}
-
-// DBStats returns database statistics.
-func (s *Storage) DBStats() sql.DBStats {
-	return s.db.Stats()
-}