ARROW-11269: [Rust] [Parquet] Preserve timezone in int96 reader

The Int96 timestamp was not using the specialised timestamp builder that takes the timezone as a paramenter.
This changes that to use the builder that preserves timezones.

I tested this change with the test file provided in the JIRA.
It looks like we don't have a way of writing int96 from the arrow writer, so there isn't an easy way to add a testcase.

Closes apache#9253 from nevi-me/ARROW-11269

Authored-by: Neville Dipale <nevilledips@gmail.com>
Signed-off-by: Neville Dipale <nevilledips@gmail.com>

rust/parquet/src/arrow/array_reader.rs

@@ -1498,7 +1498,18 @@ impl<'a> ArrayReaderBuilder {
                 arrow_type,
             )?)),
             PhysicalType::INT96 => {
-                let converter = Int96Converter::new(Int96ArrayConverter {});
+                // get the optional timezone information from arrow type
+                let timezone = arrow_type
+                    .as_ref()
+                    .map(|data_type| {
+                        if let ArrowType::Timestamp(_, tz) = data_type {
+                            tz.clone()
+                        } else {
+                            None
+                        }
+                    })
+                    .flatten();
+                let converter = Int96Converter::new(Int96ArrayConverter { timezone });
                 Ok(Box::new(ComplexObjectArrayReader::<
                     Int96Type,
                     Int96Converter,

rust/parquet/src/arrow/converter.rs

@@ -22,7 +22,6 @@ use arrow::array::{
     IntervalDayTimeArray, IntervalDayTimeBuilder, IntervalYearMonthArray,
     IntervalYearMonthBuilder, LargeBinaryBuilder, LargeStringBuilder, PrimitiveBuilder,
     PrimitiveDictionaryBuilder, StringBuilder, StringDictionaryBuilder,
-    TimestampNanosecondBuilder,
 };
 use arrow::compute::cast;
 use std::convert::{From, TryInto};
@@ -168,19 +167,19 @@ impl Converter<Vec<Option<FixedLenByteArray>>, IntervalDayTimeArray>
     }
 }
 
-pub struct Int96ArrayConverter {}
+pub struct Int96ArrayConverter {
+    pub timezone: Option<String>,
+}
 
 impl Converter<Vec<Option<Int96>>, TimestampNanosecondArray> for Int96ArrayConverter {
     fn convert(&self, source: Vec<Option<Int96>>) -> Result<TimestampNanosecondArray> {
-        let mut builder = TimestampNanosecondBuilder::new(source.len());
-        for v in source {
-            match v {
-                Some(array) => builder.append_value(array.to_i64() * 1000000),
-                None => builder.append_null(),
-            }?
-        }
-
-        Ok(builder.finish())
+        Ok(TimestampNanosecondArray::from_opt_vec(
+            source
+                .into_iter()
+                .map(|int96| int96.map(|val| val.to_i64() * 1_000_000))
+                .collect(),
+            self.timezone.clone(),
+        ))
     }
 }