Apply suggestions from code review: some safety annotations

Co-authored-by: QP Hou <dave2008713@gmail.com>

arrow/src/array/array.rs

@@ -416,6 +416,7 @@ pub fn new_null_array(data_type: &DataType, length: usize) -> ArrayRef {
                 new_null_sized_array::<IntervalDayTimeType>(data_type, length)
             }
         },
+        // Safety: `value_len` from `DataType::FixedSizeBinary` is used as data unit length value buffer length calculation
         DataType::FixedSizeBinary(value_len) => make_array(unsafe {
             ArrayData::new_unchecked(
                 data_type.clone(),

arrow/src/array/array_boolean.rs

@@ -213,6 +213,7 @@ impl<Ptr: Borrow<Option<bool>>> FromIterator<Ptr> for BooleanArray {
             }
         });
 
+        // Safety: value buffer size is derived directly from iterator size hint above
         let data = unsafe {
             ArrayData::new_unchecked(
                 DataType::Boolean,

arrow/src/array/array_primitive.rs

@@ -124,6 +124,7 @@ impl<T: ArrowPrimitiveType> PrimitiveArray<T> {
     /// Creates a PrimitiveArray based on an iterator of values without nulls
     pub fn from_iter_values<I: IntoIterator<Item = T::Native>>(iter: I) -> Self {
         let val_buf: Buffer = iter.into_iter().collect();
+        // Safety: Buffer from iterator trait is sound, generic guarantees array data type matches iterator item type
         let data = unsafe {
             ArrayData::new_unchecked(
                 T::DATA_TYPE,

arrow/src/compute/kernels/arithmetic.rs

@@ -186,6 +186,7 @@ where
     //      `values` is an iterator with a known size.
     let buffer = unsafe { Buffer::from_trusted_len_iter(values) };
 
+    // Safety: generic guarantees array data type matches with buffer value iterator datatype
     let data = unsafe {
         ArrayData::new_unchecked(
             T::DATA_TYPE,