Make more use of `stop_input_type()`

[hfrick]

Check the following candidates:

File	Line	Current message
encode_unit.R	38	"should be a numeric vector"
encode_unit.R	84	"should be a character vector"
encode_unit.R	108	"should be a numeric vector"
aaa_ranges.R	84	"should be numeric"
misc.R	149	"must be numeric"
grids.R	292-294	"must be a data frame"