v_numeric_scalar() returns a validator function that checks if a value
is a single numeric value. This is useful as a validator function for
options managers created with create_options_manager().
v_numeric_scalar()A validator function that takes a value x and raises an error
if x is not a single numeric value.
# Create a validator for numeric scalars
validator <- v_numeric_scalar()
# Valid input
validator(42)
# Invalid inputs (would raise errors)
try(validator(c(1, 2, 3))) # vector, not scalar
#> Error : must be a single numeric value
try(validator("text")) # not numeric
#> Error : must be a single numeric value