* Fix changelog entry for MSRV change in axum-extra 0.3.5
* Bump MSRV to 1.60 for axum, axum-extra, axum-macros
* Use new Cargo features to avoid implicit features for optional dependencies
* move signed cookies into their own module
* Require features for private/signed cookies
* enable "cookie" feature when enabling private/signed cookies
* add `#[cfg]`s in a few more places