Check and remove redundant operations

[karthikbhargavan]

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• [ ] https://github.com/cryspen/libcrux/blob/8cc3152db28d011f078e9e344d4421ec851cce9b/src/kem/kyber/arithmetic.rs#L68 The cast to i16 makes the call to get_n_least_significant_bits unnecessary

• [ ] https://github.com/cryspen/libcrux/blob/8cc3152db28d011f078e9e344d4421ec851cce9b/src/kem/kyber/constant_time_ops.rs#L14 The value | seems to be unnecessary

• [ ] https://github.com/cryspen/libcrux/blob/8cc3152db28d011f078e9e344d4421ec851cce9b/src/kem/kyber/constant_time_ops.rs#L54 Here the out[i] |= appears to be unnecessay. We should also check whether this masking is preserved by the compiler.