An anipoint is the position-grain frame: one row per point per
timepoint, with coordinate columns. Use is_aniframe() to test for
the whole animovement frame family instead.
Examples
af <- example_anipoint(n_obs = 3, n_individuals = 1, n_keypoints = 1)
is_anipoint(af)
#> [1] TRUE
# A plain data frame is not one
is_anipoint(data.frame(x = 1))
#> [1] FALSE