refactor: fix inference of get_cache_key

Author: AayushSabharwal

src/cache.jl

@@ -26,7 +26,20 @@ The key stored in the cache for a particular value. Returns a `SymbolicKey` for
 """
 # can't dispatch because `BasicSymbolic` isn't defined here
 function get_cache_key(x)
-    if x isa BasicSymbolic
+    @nospecialize x
+    if x isa BasicSymbolic{SymReal}
+        id = x.id
+        if id === nothing
+            return CacheSentinel()
+        end
+        return SymbolicKey(id)
+    elseif x isa BasicSymbolic{SafeReal}
+        id = x.id
+        if id === nothing
+            return CacheSentinel()
+        end
+        return SymbolicKey(id)
+    elseif x isa BasicSymbolic{SafeReal}
         id = x.id
         if id === nothing
             return CacheSentinel()