Ensure disabled tasks return full tuple & fix public‐dataset filter

[LudovicTuncay]

This PR addresses two related bugs in task scoring:

1. Disabled‐task return shape

   • Previously, when config.disabled == True, worker() returned a 3-tuple
     (formal_name, (0,0), (0,0)). Downstream code always expected a 4-tuple
     (formal_name, mlp_score, knn_score, private_flag), causing an index-out-
     of-range error when building the DataFrame.
   • Fix: Return (formal_name, (0,0), (0,0), config.private) so the shape is
     consistent in all cases.

2. Public‐dataset filter logic

   • The “public” weighted‐average was filtering on v[-1] == True, but v[-1]
     is actually the private flag. That made “public” averages include only private tasks.
   • Fix: Change the condition to if v[-1] == False so that only non-private (public)
     tasks are aggregated.

Both fixes are split into two commits for clarity. All existing tasks (and any new ones) should now pass without index errors, and the “public” averages reflect the intended data.