Fix "invalid escape sequence" errors

Starting with Python 3.12 during byte compilation the following warnings
are emitted:

	/usr/lib/python3/dist-packages/hamster/lib/datetime.py:471: SyntaxWarning: invalid escape sequence '\s'
	  position="exact", separator="\s+", default_day=None, ref="now"):
	/usr/lib/python3/dist-packages/hamster/lib/datetime.py:472: SyntaxWarning: invalid escape sequence '\s'
	  """Parse a start-end range from text.
	/usr/lib/python3/dist-packages/hamster/widgets/activityentry.py:381: SyntaxWarning: invalid escape sequence '\s'
	  fragments = [f for f in re.split("[\s|#]", text)]
	/usr/lib/python3/dist-packages/hamster/widgets/timeinput.py:141: SyntaxWarning: invalid escape sequence '\D'
	  numbers = re.split("\D", str_time)

Fix them by using raw strings or quoting as appropriate.

Author: NightTsarina

src/hamster/lib/datetime.py

@@ -468,14 +468,14 @@ def format(self, default_day=None, explicit_none=True):
 
     @classmethod
     def parse(cls, text,
-              position="exact", separator="\s+", default_day=None, ref="now"):
+              position="exact", separator=r"\s+", default_day=None, ref="now"):
         """Parse a start-end range from text.
 
         position (str): "exact" to match exactly the full text
                         "head" to search only at the beginning of text, and
                         "tail" to search only at the end.
 
-        separator (str): regexp pattern (e.g. '\s+') meant to separate the datetime
+        separator (str): regexp pattern (e.g. r'\\s+') meant to separate the datetime
                          from the rest. Discarded for "exact" position.
 
         default_day (date): If start is given without any date (e.g. just hh:mm),

src/hamster/widgets/activityentry.py

@@ -378,7 +378,7 @@ def update_suggestions(self, text=""):
                 break
 
 
-        fragments = [f for f in re.split("[\s|#]", text)]
+        fragments = [f for f in re.split(r"[\s|#]", text)]
         current_fragment = fragments[-1] if fragments else ""
 
 

src/hamster/widgets/timeinput.py

@@ -138,7 +138,7 @@ def figure_time(self, str_time):
 
         # strip everything non-numeric and consider hours to be first number
         # and minutes - second number
-        numbers = re.split("\D", str_time)
+        numbers = re.split(r"\D", str_time)
         numbers = [x for x in numbers if x!=""]
 
         hours, minutes = None, None