fix(core): handle missing entry point groups gracefully

Refactored the handling of entry points for notifiers and providers
to avoid potential errors when their groups are missing. Simplifies
and improves the robustness of the logic by directly iterating over
all entry points and filtering by group instead of relying on
potentially absent group keys.

src/trackbert/classes/core.py

@@ -74,9 +74,10 @@ class Core:
         logging.debug("Finding external notifiers")
         notifiers = []
 
-        for entry_point in importlib.metadata.entry_points().get(
+        for entry_point in importlib.metadata.entry_points():
-            "trackbert.notifiers", []
+            if entry_point.group != "trackbert.notifiers":
-        ):
+                continue
+
             logging.debug(f"Considering external notifier {entry_point.name}")
 
             try:
@@ -149,9 +150,10 @@ class Core:
 
         providers = []
 
-        for entry_point in importlib.metadata.entry_points().get(
+        for entry_point in importlib.metadata.entry_points():
-            "trackbert.providers", []
+            if entry_point.group != "trackbert.providers":
-        ):
+                continue
+
             logging.debug(f"Considering external provider {entry_point.name}")
 
             try: