Don't re-encode byte[] values in SortValues transform

[clairemcginty]

A small optimization for SortValues transform to avoid doubly roundtrip encoding values that are already byte[]s -- they can be passed directly to the Sorter.

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[clairemcginty]

This feels like a particularly inelegant solution but I didn't have a better idea 😅

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[github-actions]

Reminder, please take a look at this pr: @Abacn

[Abacn]

thanks, will take a look

[github-actions]

Reminder, please take a look at this pr: @Abacn

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[damondouglas]

Thank you for contributing this! The following three proposals go together and made more sense to provide in one comment, rather than separately. May we consider instead of the new custom class:

1. two private static methods as shown below:

private static <T> T elementOf(Coder<T> coder, byte[] bytes) throws CoderException {
    if (coder instanceof ByteArrayCoder) {
      return (T) bytes;
    }
    return CoderUtils.decodeFromByteArray(coder, bytes);
  }

  private static <T> byte[] bytesOf(Coder<T> coder, T element) throws CoderException {
    if (element instanceof byte[]) {
      return (byte[]) element;
    }
    return CoderUtils.encodeToByteArray(coder, element);
  }

2. Refactoring the SortValuesDoFn's processElement method with:

for (KV<SecondaryKeyT, ValueT> record : records) {
    sorter.add(KV.of(
        bytesOf(keyCoder, record.getKey()),
        bytesOf(valueCoder, record.getValue()))
    );
}

3. Refactoring DecodingIterator's next with:

SecondaryKeyT secondaryKey = elementOf(keyCoder, next.getKey());
ValueT value = elementOf(valueCoder, next.getValue());
return KV.of(secondaryKey, value);