Use an integer format that supports any integer.

[rvcas]

Discussed in #192

^{Originally posted by MicroProofs August 26, 2022}
Currently we use isize or might use i64 and usize or u64 for integers.

Instead we should use a Vec to hold integers and perform large number calculations in chunks of 32 bits.

The idea is for smaller numbers we should still have fast computation speed. And super large numbers are rarer.

We can use a struct that holds the Vec plus another field for positive or negative.

Thoughts?