Batch detection(test) method in FMD

[XuyangSong]

We currently have a detect(test) method to handle single flag ciphertext. Add a method to detect multiple flag ciphertexts in parallel.

[larraia]

Instead of adding a new method, we could instead pass a vector of FlagCiphertexts in the existing test function, and return a vector of bool:

fn test(dsk: &Self::DetectionKey, flag_ciphers: &[Self::FlagCiphertexts]) -> Vec<bool>;