hqc-kem: fix pkcs8 v0.11.0 API compatibility

pkcs8 v0.11.0 changed Error::KeyMalformed from a unit variant to
Error::KeyMalformed(KeyError), so passing it bare yields a function
pointer rather than an Error value.  Use pkcs8::KeyError::Invalid
instead, which converts to pkcs8::Error via From, matching the
pattern used in ml-kem.

Also bumps the pkcs8 version constraint from 0.11.0-rc.11 to 0.11
and removes the now-redundant standalone hqc-kem/Cargo.lock (the
workspace Cargo.lock is authoritative).

Author: mikelodder7