Add time-varying AR1 correlation parameter to print and tidy output

[seananderson]

Currently requires something like this:

library(sdmTMB)
fit <- sdmTMB(
  density ~ 1,
  time = "year", 
  time_varying = ~ 1,
  time_varying_type = "ar1",
  data = pcod_2011, spatial = "off", 
  spatiotemporal = "off",
  family = tweedie(link = "log")
)
p <- get_pars(fit)
rho <- 2 * plogis(p$rho_time_unscaled) - 1
rho
#>            [,1]
#> [1,] -0.8137769

^{Created on 2024-09-26 with reprex v2.1.1}