A weekend project is probably fine -- I wrote a Passkey-based SAML IdP in a weekend (re-using the SAML IdP from a different project). It's written in Tcl.
The hardest part of dealing with the Passkeys was remembering to read the whole specification before implementing it -- I spent a lot of time parsing their CBOR/COSE-based specification so that I could get the public key before "discovering" that there was a method for that defined by the specification.