Convert arguments before the call

Values from CSV files arrive as text, so every pricing function starts by converting its arguments. Write a decorator factory coerce_args(*converters): the n-th converter is applied to the n-th positional argument before the call; arguments beyond the converters, and keyword arguments, are passed unchanged. A conversion error (ValueError) reaches the caller. The starter applies it as @coerce_args(float, int) to line_total(price, quantity).