some minor changes

src/gadgets/arithmetic_u32.rs

@@ -1,7 +1,7 @@
 use alloc::string::{String, ToString};
 use alloc::vec;
 use alloc::vec::Vec;
-use plonky2::util::serialization::{IoResult, Buffer, Read, Write};
+use plonky2::util::serialization::{Buffer, IoResult, Read, Write};
 use core::marker::PhantomData;
 
 use plonky2::field::extension::Extendable;
@@ -14,7 +14,7 @@ use plonky2::plonk::circuit_builder::CircuitBuilder;
 use crate::gates::add_many_u32::U32AddManyGate;
 use crate::gates::arithmetic_u32::U32ArithmeticGate;
 use crate::gates::subtraction_u32::U32SubtractionGate;
-use crate::serialization::{WriteU32, ReadU32};
+use crate::serialization::{ReadU32, WriteU32};
 use crate::witness::GeneratedValuesU32;
 
 #[derive(Clone, Copy, Debug)]
@@ -274,7 +274,6 @@ impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F>
         out_buffer.set_u32_target(self.low, low);
         out_buffer.set_u32_target(self.high, high);
     }
-
 }
 
 #[cfg(test)]

src/gates/add_many_u32.rs

@@ -1,7 +1,7 @@
 use alloc::format;
 use alloc::string::{String, ToString};
 use alloc::vec::Vec;
-use plonky2::util::serialization::{IoResult, Buffer, Write, Read};
+use plonky2::util::serialization::{Buffer, IoResult, Read, Write};
 use core::marker::PhantomData;
 
 use itertools::unfold;

src/gates/range_check_u32.rs

@@ -216,13 +216,13 @@ impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F>
     }
 
     fn serialize(&self, dst: &mut Vec<u8>) -> IoResult<()> {
-        dst.write_usize(self.row)?;
-        self.gate.serialize(dst)
+        self.gate.serialize(dst)?;
+        dst.write_usize(self.row)
     }
 
     fn deserialize(src: &mut Buffer) -> IoResult<Self> {
-        let row = src.read_usize()?;
         let gate = U32RangeCheckGate::deserialize(src)?;
+        let row = src.read_usize()?;
         Ok(Self { row, gate })
     }
 

src/serialization.rs

@@ -14,6 +14,7 @@ impl WriteU32 for Vec<u8> {
     }
 }
 
+#[cfg(feature = "std")]
 pub trait ReadU32 {
     fn read_target_u32(&mut self) -> IoResult<U32Target>;
 }