Improve requirements traceability

[hanno-becker]

mlkem-native is an implementation of FIPS-203, FIPS-202 (partially). It also closely relates to the prior reference implementation of ML-KEM, and implements additional requirements from the FIPS 140-3 IG.

Consider ways to facilitate going from spec to implementation, implementation to spec, or implementation to implementation. This can initially be based on natural language comments, but should ideally be automated using a tool like duvet (cc @camshaft)

[camshaft]

I've opened a tracking issue to support PDFs in duvet: awslabs/duvet#166. I think the best path is to write the annotations as if duvet supported PDFs today and then once it does, we can simply just turn on reporting.