/// Build the user agent string used for requests to Lexe infrastructure at
/// compile time. We format as `<crate>/<version>`, consistent with
/// [RFC 9110 Section 10.1.5](https://datatracker.ietf.org/doc/html/rfc9110#section-10.1.5).
///
/// Example: "node/0.6.20".
/// Build the user agent string used for requests to external services at
/// compile time.
///
/// Example: "lexe-node/0.6.20".