Port to Rust edition 2024

[xiaguangbo]

https://github.com/rust-embedded/riscv/blob/master/riscv-rt/macros/src/lib.rs#L139
why not have edition = 2024? add edition = 2024 need change #[export_name = "main"] to #[unsafe(export_name = "main")]

[romancardenas]

Hi @xiaguangbo ! Thanks for raising this issue. Moving to Rust edition 2024 will need a few more tweaks, especially in macros that use no_mangle and export_name. We can try to update the edition for all our crates :)