Computes Conley (1999) spatial HAC variance-covariance matrices for models
estimated with lfe::felm() (OLS and IV/2SLS) or with
fixest's feols() (OLS and IV), feglm(), and
fepois(). For GLM fits the variance is the M-estimation sandwich
built from the stored score matrix and inverse Hessian. The spatial
meat uses a fast CSR/cumulative-score implementation in C++; see
vcovSpHAC.felm and vcovSpHAC.fixest for the
per-method argument lists.