Mark cstr_to_string as unsafe

In Rust, having an unsafe interior conventionally means that you are
guaranteeing safety at the boundary. However, that's not the case for
cstr_to_string which is taking a random pointer as input. Thankfully,
this doesn't functionally change anything anyway since it was already
always called from an unsafe context.

crates/sherpa-rs/src/lib.rs

@@ -94,8 +94,8 @@ pub struct OfflineRecognizerResult {
 
 impl OfflineRecognizerResult {
     fn new(result: &sherpa_rs_sys::SherpaOnnxOfflineRecognizerResult) -> Self {
-        let lang = cstr_to_string(result.lang);
-        let text = cstr_to_string(result.text);
+        let lang = unsafe { cstr_to_string(result.lang) };
+        let text = unsafe { cstr_to_string(result.text) };
         let count = result.count.try_into().unwrap();
         let timestamps = if result.timestamps.is_null() {
             Vec::new()

crates/sherpa-rs/src/utils.rs

@@ -4,12 +4,10 @@ pub fn cstring_from_str(s: &str) -> CString {
     return CString::new(s).expect("CString::new failed");
 }
 
-pub fn cstr_to_string(ptr: *const c_char) -> String {
-    unsafe {
-        if ptr.is_null() {
-            String::new()
-        } else {
-            std::ffi::CStr::from_ptr(ptr).to_string_lossy().into_owned()
-        }
+pub unsafe fn cstr_to_string(ptr: *const c_char) -> String {
+    if ptr.is_null() {
+        String::new()
+    } else {
+        std::ffi::CStr::from_ptr(ptr).to_string_lossy().into_owned()
     }
 }