firpo_inf: Get the permutation distribution of the test stat assuming...
In ebenmichael/ents: Maximum Entropy Synthetic Controls

Get the permutation distribution of the test stat assuming equal probability of treatment

1 2	firpo_inf(metadata, fitfunc, units, trt_unit, pretimes, posttimes, statfuncs, include_treat)

`metadata`	with treatment time
`fitfunc`	Partially applied fitting function which takes in the number of the treated unit
`units`	Numbers of the units to permute treatment around
`trt_unit`	Treated unit
`pretimes`	Vector of times in pre-period
`posttimes`	Vector of times in post-period
`statfuncs`	Function to compute test stats
`include_treat`	Whether to include the treated unit