I have no affiliation, I'm just a commenter.

The standard library requires a heap and such, but you can enable the no_std attribute to work in environments where they don't exist. https://docs.rust-embedded.org/book/intro/no-std.html

Rust's safety model only applies to code you write in your program, and there's a lot that's unsafe (cannot be verified by the compiler) about writing a kernel or a firmware, agreed. You could have similar problems when doing FFI as well.