Fixed critical bug in as_hrf() where parameters stored in the params attribute were never used at evaluation time (#). Previously, calling as_hrf(hrf_gamma, params = list(shape = 8, rate = 1.2)) would create an HRF that used the default parameter values instead of the specified ones. This caused hrf_library() to produce perfectly collinear basis functions when different parameters were provided. The fix creates a closure that properly captures and applies parameters during evaluation.