libcrux: Panic in Signature Hint Decoding During Verification

Summary

During ML-DSA verification the serialized hint values are decoded as specified in algorithm 22 `HintBitUnpack` of [FIPS 204, subsection 7.1](https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.204.pdf#%5B%7B%22num%22%3A120%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22FitH%22%7D%2C657%5D). The algorithm requires that the cumulative hint counters per row of the hint vector are strictly increasing and below a maximum value which depends on the choice of ML-DSA parameter set (line 4). In libcrux-ml-dsa, hint decoding did not check the boundedness of the cumulative hint counter of the last row of the hint vector. ## Impact A manipulated invalid hint can cause an out-of-bounds memory access since the hint decoding logic may attempt to read outside the bounds of the serialized signature, causing a runtime panic. ## Mitigation Starting from version `0.0.8`, hint decoding will check the cumulative hint counter of the last row as well.