Optional post-processing for VatchexGreece.fetch/1 results.

Reshapes the raw GSIS response map into a more ergonomic form:

• Adds afm_full derived from afm.
• Combines postal address fields into a %{street_address: ..., raw: ...} submap.
• Adds is_active derived from stop_date.

• Reshapes activities list into %{primary: map | nil, secondary: [maps]}.

Pass pretty: true to fetch/1 to apply this automatically.