fix: Ensure timestamp conversion errors are surfaced

Explicitly call `dt_to_pb_timestamp_utc` for start_time and end_time.

Previously, an error during this conversion might not have been handled
explicitly at this point. This change guarantees that if the conversion
fails, the exception is propagated immediately, improving robustness and
aiding debugging by making the failure point clear.

Signed-off-by: Matthias Wende <[email protected]>

Author: matthias-wende-frequenz

src/frequenz/client/electricity_trading/_client.py

@@ -1036,6 +1036,9 @@ def receive_public_order_book(
             side=side,
         )
 
+        start_time_utc = dt_to_pb_timestamp_utc(start_time) if start_time else None
+        end_time_utc = dt_to_pb_timestamp_utc(end_time) if end_time else None
+
         if (
             public_order_filter not in self._public_orders_streams
             or not self._public_orders_streams[public_order_filter].is_running
@@ -1047,16 +1050,8 @@ def receive_public_order_book(
                         lambda: self.stub.ReceivePublicOrderBookStream(
                             electricity_trading_pb2.ReceivePublicOrderBookStreamRequest(
                                 filter=public_order_filter.to_pb(),
-                                start_time=(
-                                    dt_to_pb_timestamp_utc(start_time)
-                                    if start_time
-                                    else None
-                                ),
-                                end_time=(
-                                    dt_to_pb_timestamp_utc(end_time)
-                                    if end_time
-                                    else None
-                                ),
+                                start_time=start_time_utc,
+                                end_time=end_time_utc,
                             ),
                             metadata=self._metadata,
                         ),