Allow empty `ConsistentPermutation`

Is there any reason `ConsistentPermutation` doesn't allow `n` to be zero - as per [this assertion](https://github.com/github/rust-gems/blob/main/crates/consistent-choose-k/src/consistent_permutation.rs#L156).

This results in special casing when you're constructing the permutations. We might need a branch at the top of the `next` function to check, but it should be highly predictable.

从 crates/consistent-choose-k/src/consistent_permutation.rs 开始，重点查看第 156 行的 assertion 以及 issue 中提到的下一个函数。验证当前如何处理 n = 0，并确认无需在调用方进行特殊处理即可构造空排列。

由索引模型根据 Issue 内容生成。