Gets the `n`-th Ristretto point.

The `n`-th Ristretto point is defined as:

```text
if n == 0 {
    one_commit = curve25519_dalek::ristretto::RistrettoPoint::identity();
} else {
    one_commit[0] = g[0] + g[1] + ... + g[n - 1];
}
```

where `g[i]` is the `i`-th generator provided by `get_curve25519_generators` function at the offset `0`.

# Arguments

* `n` - the `n`-th Ristretto point to be fetched.

# Return

The `n`-th Ristretto point defined as above.

# Panics

If the compute `get_one_curve25519_commit` execution in the GPU / CPU fails.