Function parse_key_value 

fn parse_key_value(
    token: &str,
) -> Result<(VariableValue, u32), MappingParseError>

Parse the value part of the first item into a VariableValue` and its bit width.

For binary strings and nine-value strings, the bit width is determined by the string length. For hex, octal, and decimal numbers, the bit width is determined by the number of bits required to represent the actual numeric value.