Modularized PSQ

[jschneider-bensch]

This PR modularizes the PSQ protocol into

• a PSQ-component generation module: A minimal version of the previous PSQ protocol, deriving a "Pre-PSK" by encapsulating towards the receiver using PQ-KEM and then working in outer protocol context into the shared secret.
• A protocol binder that makes use of the PSQ-component generation to bind to incorporate outer protocol requirements, e.g. a PSK time to live or binding / authenticating other material. This is exemplified here by a binder for ECDH based-protocols with PSK-TTL.

[franziskuskiefer]

Thanks! lgtm in general. I left some comments on the code (not protocol, that looks fine).

[jschneider-bensch]

We know the content (or its size, rather) of the AEAD ciphertext as well, so I could use the non-allocating API there, too.
But I found that a bit weird to use, since you have to allocate a buffer for ciphertext and tag, and it returns the tag as well.

Review re-requested

[franziskuskiefer]

lgtm, let's get this in and then iterate.

It would be great if you would add a usage example in the lib docs os there's an easy starting point.