Rework conversation data types and make safe wrappers. This removes the old `Conversation` type and reworks the FFI types used for PAM conversations. This creates safe `TestResponse` and `BinaryResponse` structures in `conv`, providing a safe way to pass response messages to PAM Conversations. The internals of these types are allocated on the C heap, as required by PAM. We also remove the Conversation struct, which was specific to the real PAM implementation so that we can introduce a better abstraction. Also splits a new `PamApplicationHandle` trait from `PamHandle`, for the parts of a PAM handle that are specific to the application side of a PAM transaction.

[package]
name = "nonstick"
description = "PAM bindings for Rust"
version = "0.0.6"
authors = ["Paul Fisher <paul@pfish.zone>", "Anthony Nowell <anowell@gmail.com>" ]
repository = "https://hg.pfish.zone/crates/nonstick/"
readme = "README.md"
keywords = ["pam", "ffi", "linux", "authentication"]
license = "MIT"
edition = "2021"

[features]
experimental = []

[dependencies]
bitflags = "2.9.0"
libc = "0.2.97"
num-derive = "0.4.2"
num-traits = "0.2.19"
secure-string = "0.3.0"
thiserror = "2.0.12"