Fix serialize feature in rust crate flatbuffers

rust/flatbuffers/src/array.rs

@@ -149,7 +149,7 @@ where
     T: 'a + Follow<'a>,
     <T as Follow<'a>>::Inner: serde::ser::Serialize,
 {
-    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
+    fn serialize<S>(&self, serializer: S) -> core::result::Result<S::Ok, S::Error>
     where
         S: serde::ser::Serializer,
     {

rust/flatbuffers/src/builder.rs

@@ -1228,12 +1228,14 @@ impl<T> IndexMut<ReverseIndexRange> for [T] {
 mod tests {
     use super::*;
     use core::sync::atomic::{AtomicUsize, Ordering};
+    #[cfg(feature = "std")]
     use std::alloc::{GlobalAlloc, Layout, System};
 
     static ALLOC_COUNT: AtomicUsize = AtomicUsize::new(0);
 
     struct CountingAllocator;
 
+    #[cfg(feature = "std")]
     unsafe impl GlobalAlloc for CountingAllocator {
         unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
             ALLOC_COUNT.fetch_add(1, Ordering::Relaxed);
@@ -1244,6 +1246,7 @@ mod tests {
         }
     }
 
+    #[cfg(feature = "std")]
     #[global_allocator]
     static GLOBAL: CountingAllocator = CountingAllocator;
 

rust/flatbuffers/src/vector.rs

@@ -337,7 +337,7 @@ where
     T: 'a + Follow<'a>,
     <T as Follow<'a>>::Inner: serde::ser::Serialize,
 {
-    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
+    fn serialize<S>(&self, serializer: S) -> core::result::Result<S::Ok, S::Error>
     where
         S: serde::ser::Serializer,
     {