Format numbers for better readability

[f0i]

Enforce the [style guide recommendation](https://internetcomputer.org/docs/current/developer-docs/build/cdks/motoko-dfinity/style/#miscellaneous] for numbers:

Group by 3 digits in decimal numbers and by 4 in hexadecimal notation.

In addition, add leading zeros in hex notation to be 2 digits or a multiple of 4 digits.

Examples:

• 1000000 would be formatted as 1_000_000
• 0x2 would be formatted as 0x02
• 0x123456 would be formatted as 0x0012_3456
• 12_34_56 would be formatted as 123_456
• 0.123456 would be formatted as 0.123_456