migrate from PyQt6 to PySide6, remove unneeded dependencies

src/ui/widgets/calendar_entry.py

@@ -1,15 +1,13 @@
 from .widget_sources.calendar_entry_ui import Ui_Dialog
-from PyQt6 import QtWidgets
-from PyQt6.QtCore import pyqtSignal
+from PySide6 import QtWidgets
+from PySide6.QtCore import Signal
 from src.backend.database import Database
 from src import Icon
 
 
 class CalendarEntry(QtWidgets.QDialog, Ui_Dialog):
-    deleteSignal = pyqtSignal(
-        int
-    )  # when emit, send the id of the message to be deleted
-    repaintSignal = pyqtSignal(str)
+    deleteSignal = Signal(int)  # when emit, send the id of the message to be deleted
+    repaintSignal = Signal(str)
 
     def __init__(self, parent=None, messages=None, date=None):
         super().__init__(parent)