GH-343: Fix ListVector offset buffer not properly serialized for nested empty arrays (#967)

## What's Changed

Fix `ListVector`/`LargeListVector` IPC serialization when `valueCount`
is 0.

### Problem

When `valueCount == 0`, `setReaderAndWriterIndex()` was setting
`offsetBuffer.writerIndex(0)`, which means `readableBytes() == 0`. IPC
serializer uses `readableBytes()` to determine buffer size, so 0 bytes
were written to the IPC stream. This crashes IPC readers in other
libraries because Arrow spec requires offset buffer to have at least one
entry `[0]`.

@viirya:

> The offset buffers are allocated properly. But during IPC
serialization, they are ignored.
> ```
>   public long readableBytes() {
>       return writerIndex - readerIndex;
>   }
> ```
> So when ListVector.setReaderAndWriterIndex() sets writerIndex(0) and
readerIndex(0), readableBytes() returns 0 - 0 = 0.
> 
> Then when MessageSerializer.writeBatchBuffers() calls
WriteChannel.write(buffer), it writes 0 bytes.
>
> So the flow is:
> 
> valueCount=0 → ListVector.setReaderAndWriterIndex() sets
offsetBuffer.writerIndex(0)
> VectorUnloader.getFieldBuffers() returns the buffer with writerIndex=0
> MessageSerializer.writeBatchBuffers() writes the buffer
> WriteChannel.write(buffer) checks buffer.readableBytes() which is 0
> 0 bytes are written to the IPC stream
> PyArrow read the batch with the missing buffer → crash when other
libraries to read

### Fix

Simplify `setReaderAndWriterIndex()` to always use `(valueCount + 1) *
OFFSET_WIDTH` for offset buffer's `writerIndex`. When `valueCount == 0`,
this correctly sets `writerIndex` to `OFFSET_WIDTH`, ensuring
`offset[0]` is included in serialization.

### Testing

Added tests for nested empty lists verifying offset buffer has correct
`readableBytes()`.

Closes #343.

---------

Co-authored-by: Yicong Huang <yicong.huang+data@databricks.com>