buffer_sv2: is a no_stdcrate by default

- only feature `debug` will add `std` dep which is not used by any other crates
- just had to replace `std::hint` by its `core` equivalent
- in `debug` removed a `mut` to clear a warning

utils/buffer/src/buffer_pool/mod.rs

@@ -606,7 +606,7 @@ impl<T: Buffer> Buffer for BufferPool<T> {
                     "{} {} {}",
                     self.inner_memory.raw_offset, self.inner_memory.raw_len, self.inner_memory.len
                 );
-                let mut res = self.inner_memory.get_data_owned(shared_state, mode);
+                let res = self.inner_memory.get_data_owned(shared_state, mode);
                 self.pool_back
                     .set_len_from_inner_memory(self.inner_memory.len);
                 println!(
@@ -684,7 +684,7 @@ impl<T: Buffer> Buffer for BufferPool<T> {
 impl<T: Buffer> Drop for BufferPool<T> {
     fn drop(&mut self) {
         while self.shared_state.load(Ordering::Relaxed) != 0 {
-            std::hint::spin_loop();
+            core::hint::spin_loop();
         }
     }
 }

utils/buffer/src/lib.rs

@@ -1,4 +1,4 @@
-//#![cfg_attr(not(feature = "debug"), no_std)]
+#![cfg_attr(not(feature = "debug"), no_std)]
 //#![feature(backtrace)]
 
 mod buffer;