var_Lip: Lipschitz class variance
In koohyun-kwon/HTEBand: Uniform confidence band for heterogenous treatment effects

Calculates the variance for regression function value estimator under Lipschitz class

1	var_Lip(y, x, t, kern, h, deg = NULL, sd.homo = TRUE)

`y`	vector of dependent variables
`x`	a vector of regressors.
`t`	a scalar evaluation point.
`kern`	a string for kernel name; currently `"tri"` is supported.
`h`	a positive bandwidth.
`deg`	degree of local polynomial regression to be used
`sd.homo`	logical indicating whether the variance would be estimated under locally homoskedastic variance assumption; the default is `sd.homo = TRUE`.