chore(core/rust): bump cstr_core, enable nightly features

So that cstr! can be used in const contexts. This is not critical but it's nice-to-have as long as we are on nightly anyway.

core/embed/rust/Cargo.lock

@@ -73,9 +73,9 @@ dependencies = [
 
 [[package]]
 name = "cstr_core"
-version = "0.2.4"
+version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "917ba9efe9e1e736671d5a03f006afc4e7e3f32503e2077e0bcaf519c0c8c1d3"
+checksum = "dd98742e4fdca832d40cab219dc2e3048de17d873248f83f17df47c1bea70956"
 dependencies = [
  "cty",
  "memchr",

core/embed/rust/Cargo.toml

@@ -90,8 +90,9 @@ default_features = false
 version = "0.3.3"
 
 [dependencies.cstr_core]
-version = "0.2.4"
-default_features = false
+version = "0.2.6"
+default-features = false
+features = ["nightly"]
 
 # Build dependencies
 

core/embed/rust/src/error.rs

@@ -29,7 +29,7 @@ pub enum Error {
 #[macro_export]
 macro_rules! value_error {
     ($msg:expr) => {
-        Error::ValueError(cstr!($msg))
+        Error::ValueError(cstr_core::cstr!($msg))
     };
 }
 

core/embed/rust/src/protobuf/error.rs

@@ -2,13 +2,11 @@ use cstr_core::cstr;
 
 use crate::{error::Error, micropython::qstr::Qstr};
 
-// XXX const version of `from_bytes_with_nul_unchecked` is nightly-only.
-
-pub fn experimental_not_enabled() -> Error {
+pub const fn experimental_not_enabled() -> Error {
     value_error!("Experimental features are disabled.")
 }
 
-pub fn unknown_field_type() -> Error {
+pub const fn unknown_field_type() -> Error {
     value_error!("Unknown field type.")
 }
 
@@ -20,6 +18,6 @@ pub fn invalid_value(field: Qstr) -> Error {
     Error::ValueErrorParam(cstr!("Invalid value for field."), field.into())
 }
 
-pub fn end_of_buffer() -> Error {
+pub const fn end_of_buffer() -> Error {
     value_error!("End of buffer.")
 }

core/embed/rust/src/trezorhal/storage.rs

@@ -3,7 +3,7 @@
 use super::ffi;
 use crate::error::Error;
 use core::ptr;
-use cstr_core::{cstr, CStr};
+use cstr_core::CStr;
 
 /// Result of PIN delay callback.
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]

core/embed/rust/src/ui/layout/util.rs

@@ -18,7 +18,6 @@ use crate::{
         util::set_animation_disabled,
     },
 };
-use cstr_core::cstr;
 use heapless::Vec;
 
 #[cfg(feature = "jpeg")]

core/embed/rust/src/ui/model_tt/layout.rs

@@ -1,5 +1,4 @@
 use core::{cmp::Ordering, convert::TryInto};
-use cstr_core::cstr;
 
 use crate::{
     error::Error,