Add bool types to Rust coding standards guidelines

Similar to #25368 (moved), we can once again expand upon which Rust types are safe to send over the FFI boundary without conversion/serialisation/translation, because Rust's bool type and C99's bool type are directly compatible. (I think this also makes an even larger argument moving forward for using bools in C wherever it makes sense, since otherwise we need to convert between the libc uint8_t type and the native u8 in Rust.)