Added `sec[bool]` and `sec[f64]`

[bvssvni]

Closes #367, fixes a bug in the lifetime checker #374

This PR adds sec[bool] and sec[f64] types, which improves type safety for secrets and makes it easier to generate efficient Rust code from Dyon in the future.

What is a secret?

A secret is a "hidden" array that is associated with a bool or f64. It is used to make problem solving easier by integrating this with mathematical loops in Dyon.

For example, to look up where a maximum value comes from:

fn main() {
    list := [[1, 2], [3, 4]]
    item := 0
    max := max i, j {
        item = list[i][j]
        if item == 4 { continue }
        item
    }
    println(max) // prints `4`
    println(where(max)) // prints `[1, 0]`
}

Dyon uses index notation for mathematical loops, such that the argument of any/all/min/max compositions of loops can be propagated as a secret.