55 move low level webauthn logic to primitives directory

[JohnGuilding]

This PR:

1. Adds a new foundry project inside the primitives directory
2. Moves webauthn contract and accompanying libraries to primitives directory (including test)
3. Symlinks primitives to account-integrations/safe
4. Deletes old files in the safe directory
5. Adds a github workflow for primitives

[blakecduncan]

Nice! This lgtm!

[jzaki]

On the cryptographic side (before here) is client challenge always guaranteed to be 32 bytes?

[JohnGuilding]

Good question, I've seen bytes32 used elsewhere, but looking at the spec itself, it looks like the challenge should be a minimum of 16 bytes, so it could be different to 32 bytes:

In order to prevent replay attacks, the challenges MUST contain enough entropy to make guessing them infeasible. Challenges SHOULD therefore be at least 16 bytes long.

https://www.w3.org/TR/webauthn-2/#sctn-cryptographic-challenges

FCL assumes bytes32 but perhaps this is wrong according to the spec. Added an issue to look into this - #107

[jzaki]

Would be good to know how much of account-integrations/safe/SafeWebAuthnPlugin can make its way into primitives/WebAuthn and remain generic to 4337.
@blakecduncan this could be explored in bringing WebAuthn into account-integrations/kernel (lower priority than current integration work)