Remove redundant memory management in nonstick::libpam; fix UB. - Uses the libpam-sys-helpers BinaryPayload / OwnedBinaryPayload structs to handle memory management and parsing for Linux-PAM binary messages. - Gets rid of the (technically) undefined behavior in PtrPtrVec due to pointer provenance. - Don't check for malloc failing. It won't, even if it does. - Formatting/cleanups/etc.