calculate site spacing for npx 2.0 compatibility

[eggriel]

add function load_channel_position to change site spacing accordingly. Site spacing is different for npx 1.0 and npx 2.0.

[jsiegle]

Hi @eggriel -- currently site spacing is specified as part of the input JSON (schema definition here). It looks like you're trying to load this from the first two rows of the channel_positions.npy file instead. One issue I foresee with this approach is that if an alternate electrode configuration is selected, the distance between the first two rows might not be equal to the actual electrode spacing. So it's probably safer to specify the spacing in the JSON file, based on the known electrode type. Is there a reason you'd like to avoid this?