chore: All of vortex-gpu requires compiler flag (#5362)

Signed-off-by: Robert Kruszewski <github@robertk.io>

Author: robert3005

vortex-gpu/src/gpu_array.rs

@@ -117,7 +117,7 @@ impl GpuPrimitiveVector {
             let mut buffer = BufferMut::<P>::with_capacity(self.len);
             unsafe { buffer.set_len(self.len) }
             stream
-                .memcpy_dtoh(&self.as_slice::<P>(), &mut buffer[..])
+                .memcpy_dtoh(&self.as_slice::<P>(), &mut buffer)
                 .map_err(|e| vortex_err!("Failed to copy to device: {e}"))?;
             stream
                 .synchronize()

vortex-gpu/src/lib.rs

@@ -8,6 +8,7 @@
 //! ```shell
 //! RUSTFLAGS="--cfg gpu_unstable" cargo build -p ...
 //! ```
+#![cfg(gpu_unstable)]
 
 pub mod bit_unpack;
 pub mod for_;

vortex-gpu/src/take.rs

@@ -114,7 +114,7 @@ where
     unsafe { buffer.set_len(codes.len()) }
 
     stream
-        .memcpy_dtoh(&cu_out, &mut buffer[..])
+        .memcpy_dtoh(&cu_out, &mut buffer)
         .map_err(|e| vortex_err!("Failed to copy to device: {e}"))?;
     stream
         .synchronize()