Terran add-ons have an overly large footprint_radius

The Terran add-on buildings (like the barracks reactor) report an overly large `footprint_radius` in the returned `AbilityData` from the game. Here's an example (in json format):

```json
{
"ability_id": 422,
"link_name": "BarracksAddOns",
"link_index": 1,
"button_name": "Reactor",
"friendly_name": "Build Reactor Barracks",
"hotkey": "C",
"remaps_to_ability_id": 3683,
"target": "PointOrNone",
"available": true,
"allow_minimap": false,
"allow_autocast": false,
"is_building": true,
"footprint_radius": 3.5,
"is_instant_placement": true,
"cast_range": 0.0
}
```

I'm not sure if the correct value should be `1.0` (for the add-on only), or maybe `2.5` (if including the footprint of the barracks)

Start by locating the AbilityData definition and the handling of the footprint_radius field in the protocol sources. Compare the reported Terran add-on value with the relevant game data and determine the correct footprint semantics; done means the returned AbilityData reports the expected radius for add-on buildings.

Written by the indexing model from the issue text.