Voltage interpolation for samplers, detectors, and point processes.

[halfflat]

In the FVM discretized cells, a voltage sample, threshold detector, or point process will see the voltage associated with the control volume, effectively making the voltage approximation piecewise constant in space.

We may be able to improve accuracy with a small overhead by using linear interpolants of the voltage.

Tasks

1. Characterize current accuracy penalty due to spatial discretization without interpolation.
2. Implement interpolated voltage sampling and compare.
3. Evaluate benefits of using an interpolated voltage for threshold detection and synapses. Should synapses interpolate voltage but contribute only to one CV, or contribute via a weight to neighbouring CVs?
4. Implement (3) efficiently if benefits are worth it. For linearly coalesced synapses, this may involve associating contribution weights with the back-end target identifiers.