"unknown algorithm" error

Using ssh-key to create a new PrivateKey using an algorithm which doesn't have the correct crate feature enabled results in a runtime error (unknown algorithm).

The following code compiles fine but panics with an error at runtime.

# Cargo.toml
[dependencies]
ssh-key = "0.6"

// main.rs
use ssh_key::rand_core::OsRng;
use ssh_key::{Algorithm, PrivateKey};

fn main() {
    let private_key = PrivateKey::random(&mut OsRng, Algorithm::Ed25519).unwrap();
    dbg!(&private_key);
}

This is not very rusty. It would be much less surprising if the enum variant Ed25519 of the Algorithm enum would also be guarded by the feature that enables the algorithm.

Start with the Algorithm enum and the PrivateKey::random entry point, using the Cargo.toml and main.rs example to reproduce the runtime error. Trace how algorithm features are defined and gated, then verify that an unavailable algorithm cannot compile or is otherwise rejected before the current "unknown algorithm" runtime failure.