Migrate to clap 4.2, run binaries/examples with --help in CI, and clean up examples

[micolous]

There was an issue with clippy throwing correctness errors on Rust 1.69 for clap 3.2.x's macros, so I had previously disabled it. Migrating to clap 4.x fixes this, so we can re-enable clippy in CI.

clap 4.x has a few API changes, the main one for us was that it now the original struct field name as a field ID, rather than the "normalised" form (changing _ to -), so conflicts_with_all and ArgGroups need updating. It also looks like some parts of clap only check argument definitions at runtime, and errors don't show up with cargo test; so we need to run those binaries manually with --help to discover errors.

While here, I've done some house-keeping on many webauthn-authenticator-rs examples:

• rename authenticate/main.rs to authenticate.rs
• rename cable_domain/main.rs to cable_domain.rs
• cable_tunnel example now uses required-features in Cargo.toml; so cable_tunnel/main.rs is gone, and effectively renaming cable_tunnel/core.rs to cable_tunnel.rs. This also fixes a broken link in the cable-tunnel-server README.
• delete obsolete nfc_token_info example, as fido-key-manager can do the same thing
• rename softtoken/main.rs to softtoken.rs

Fixes #313

• cargo test has been run and passes
• documentation has been updated with relevant examples (if relevant)