chore(swarm): move swarm-nats-auth's deps to the workspace

Per mara on the PR: all deps go into workspace level so versions stay
consistent. async-nats, data-encoding, nkeys and nats-jwt are new
[workspace.dependencies] entries; sha2 and futures-util now come from
there.

The crate had asked for sha2 0.10 while the workspace standard is 0.11,
and for the futures facade where the workspace carries futures-util. Both
resolved without adding a Cargo.lock entry - each was already in the tree
via something else - so the drift was invisible in the lock and would only
have surfaced as two versions of a hashing crate in one binary.

swarm-nats-auth/src/main.rs

@@ -25,7 +25,7 @@ use std::path::PathBuf;
 
 use anyhow::Context;
 use clap::Parser;
-use futures::StreamExt;
+use futures_util::StreamExt;
 
 mod introspect;
 mod request;