Do not submit profile lookups to worldgen threads

They block. On network I/O.

If enough tasks are submitted the server will eventually stall
out due to a sync load, as the worldgen threads will be
stalling on profile lookups.

paper-server/patches/sources/net/minecraft/world/level/block/entity/SkullBlockEntity.java.patch

@@ -0,0 +1,11 @@
+--- a/net/minecraft/world/level/block/entity/SkullBlockEntity.java
++++ b/net/minecraft/world/level/block/entity/SkullBlockEntity.java
+@@ -105,7 +105,7 @@
+                 ProfileResult profileResult = apiServices.sessionService().fetchProfile(uuid, true);
+                 return Optional.ofNullable(profileResult).map(ProfileResult::profile);
+             }
+-        }, Util.backgroundExecutor().forName("fetchProfile"));
++        }, Util.PROFILE_EXECUTOR); // Paper - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
+     }
+ 
+     public static void clear() {