ml-kem: zeroize seed value of DecapsulationKey on drop

[MGibson1]

FIPS 203 section 3.3 Destruction of intermediate values:

The seed (𝑑, 𝑧) generated in steps 1 and 2 of ML-KEM.KeyGen can be stored for later
expansion using ML-KEM.KeyGen_internal. As this seed can be used to compute the
decapsulation key, it is sensitive data and shall be treated with the same safeguards as a
decapsulation key (see SP 800-227 [1]).

Since decapsulation keys are zeroized on drop, 𝑑 should be, to

[tarcieri]

Good find, thanks