Ensure that allocated channels are reserved.

This was previously mostly working because the allocator itself was
moving forward, but since each radio has its own allocator, aircraft
with different radios would often get overlapping intra-flight
frequencies.

gen/radios.py

@@ -183,6 +183,7 @@ class RadioRegistry:
         try:
             while (channel := next(allocator)) in self.allocated_channels:
                 pass
+            self.reserve(channel)
             return channel
         except StopIteration:
             raise OutOfChannelsError(radio)