fixup! Implement GetMicrogridMetadata

Add active_at() method and use timezone-aware timestamps.

Author: llucax

src/frequenz/client/microgrid/_lifetime.py

@@ -5,7 +5,7 @@
 
 
 from dataclasses import dataclass
-from datetime import datetime
+from datetime import datetime, timezone
 from functools import cached_property
 
 
@@ -36,10 +36,24 @@ def __post_init__(self) -> None:
         if self.start is not None and self.end is not None and self.start > self.end:
             raise ValueError("Start must be before or equal to end.")
 
+    def active_at(self, timestamp: datetime) -> bool:
+        """Check whether this lifetime is active at a specific timestamp.
+
+        Args:
+            timestamp: The timestamp to check activity for.
+
+        Returns:
+            True if active at the given timestamp, False otherwise.
+        """
+        # Handle start time - it's not active if start is in the future
+        if self.start is not None and self.start > timestamp:
+            return False
+        # Handle end time - active up to and including end time
+        if self.end is not None:
+            return self.end >= timestamp
+        return True
+
     @cached_property
     def active(self) -> bool:
         """Whether this lifetime is currently active."""
-        now = datetime.now()
-        if self.start is not None and self.start > now:
-            return False
-        return self.end is None or self.end >= now
+        return self.active_at(datetime.now(timezone.utc))