An alternative implementation to spdep::localG intended for use with
a spacetime cube.

## Usage

`local_g_spt(x, times, nb, wt, n_locs, nsim)`

## Arguments

- x
a numeric vector

- times
a vector determining time order

- nb
a spacetime neighbors list

- wt
a weights list associated with `nb`

- n_locs
the number of unique locations

- n_sim
the number of simulations to run for calculating `p_sim`