Use getFromNamespace instead of ::: to fix S3 dispatch for as_gt()

[jdblischak]

Avoid R CMD check NOTE about accessing internal functions between packages we maintain (in this case {gsDesign2})

xref: #284, #287, Merck/gsDesign2#490, Merck/gsDesign2#492

[jdblischak]

Demonstration that it still works:

library("gsDesign2")
library("simtrial")
## Attaching package: ‘simtrial’
##
## The following object is masked from ‘package:gsDesign2’:
##
##     as_gt
##

# works without gsDesign2:: prefix
gs_design_ahr() |> summary() |> as_gt()
fixed_design_ahr(
  enroll_rate = define_enroll_rate(duration = 18, rate = 1),
  fail_rate = define_fail_rate(
    duration = c(4, 100),
    fail_rate = log(2) / 12,
    hr = c(1, .6),
    dropout_rate = .001
  )
) |> summary() |> as_gt()

[jdblischak]

All the builds returned no NOTEs. Though in this case there was no NOTE beforehand, presumably because the dev version of {gsDesign2} is being installed (#297). It seems that it is ok with ::: as long as the internal function exists. Still safer to use getFromNamespace() though to avoid any potential problems during CRAN submission

[LittleBeannie]

Thank you, @jdblischak !