Move away from `rustls-pemfile`

[Frando]

rustls-pemfile is unmaintained: https://rustsec.org/advisories/RUSTSEC-2025-0134
#3744 adds an exception to our deny.toml

Migration to rustls-pki-types is simple in princple. However, we have a couple of dependencies that also use rustls-pemfile:

• axum-server, used in iroh-dns-server: Fixed in axum-server@0.8.0 - but we need to match the version in tokio-rustls-acme
• tokio-rustls-axum: deps!: bump axum-server tokio-rustls-acme#37
• rustls-cert-file-reader: I filed deps: remove rustls-pemfile MOZGIII/rustls-cert-utils#22

[MOZGIII]

rustls-cert-file-reader is ready 🚀