✨(api) check if cache changed before adding a cache entry

Prolonged computation times for certain indicators can bring redundant cache
entries from parallel computations.
Before adding a cache entry, we now check if an identical one already exists,
similar to Django's `get_or_create` mechanism.

src/api/core/warren/indicators/mixins.py

@@ -136,6 +136,9 @@ async def get_or_compute(self, update: bool = False):
         if issubclass(self._compute_annotation, BaseModel):
             value = value.json()
 
+        # Cache entry may have been created during a long compute time
+        cache = await self.get_cache()
+
         if cache is None:
             cache = CacheEntry.parse_obj(
                 CacheEntryCreate(key=self.cache_key, value=value)