Move internal packages to an internal folder

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

internal/model/user_session.go

@@ -0,0 +1,40 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package model // import "miniflux.app/v2/internal/model"
+
+import (
+	"fmt"
+	"time"
+
+	"miniflux.app/v2/internal/timezone"
+)
+
+// UserSession represents a user session in the system.
+type UserSession struct {
+	ID        int64
+	UserID    int64
+	Token     string
+	CreatedAt time.Time
+	UserAgent string
+	IP        string
+}
+
+func (u *UserSession) String() string {
+	return fmt.Sprintf(`ID="%d", UserID="%d", IP="%s", Token="%s"`, u.ID, u.UserID, u.IP, u.Token)
+}
+
+// UseTimezone converts creation date to the given timezone.
+func (u *UserSession) UseTimezone(tz string) {
+	u.CreatedAt = timezone.Convert(tz, u.CreatedAt)
+}
+
+// UserSessions represents a list of sessions.
+type UserSessions []*UserSession
+
+// UseTimezone converts creation date of all sessions to the given timezone.
+func (u UserSessions) UseTimezone(tz string) {
+	for _, session := range u {
+		session.UseTimezone(tz)
+	}
+}