Systemd 263 adds Rust support for new modules

Systemd 263 has merged patches that let new modules be written in Rust. Existing C code is not being ported, builds use Meson instead of cargo, and Rust code avoids the standard library. Requirements are Rust 1.85+, bindgen 0.71.1 and Meson 1.4.0.

• Rust is used only for new leaf components; existing C code is not ported
• Builds run through Meson, with no cargo involved
• Requirements: Rust 1.85+, bindgen 0.71.1, Meson 1.4.0
• Rust in systemd's core was deferred over dynamic library support