"literal BigInt values should be bolded" rule doesn't catch all cases

[ptomato]

I've noticed that this rule catches 1000<sub>ℤ</sub> (which should be *1000*<sub>ℤ</sub>) but fails to catch scientific notation like 10<sup>3</sup><sub>ℤ</sub> or −8.64 × 10<sup>21</sup><sub>ℤ</sub>.