refactor(handler): Guard type hints imports with TYPE_CHECKING

Author: gfieni

src/powerapi/handler/handler.py

@@ -27,8 +27,14 @@
 # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 from powerapi.exception import PowerAPIException, UnknownMessageTypeException
-from powerapi.actor.message import Message
+
+if TYPE_CHECKING:
+    from powerapi.actor.message import Message
 
 
 class HandlerException(PowerAPIException):