Revise capacity for candidate assets

Annoyingly, the prices are unreliable with ca capacity set to anything less than 0.00001. So let's stick with 0.0001 for now. This is odd, must be something to do with the solver tolerance or similar. There's probably a switch or value to set that could fix it, but I' don't know what it is. Issue here is that a user might actually try to work with very low capacity values.

_Originally posted by @ahawkes in https://github.com/EnergySystemsModellingLab/MUSE_2.0/issues/671#issuecomment-3023636953_