ParquetWriter should account for the buffer of the inner writer when checking `current_written_size`

[CTTY]

Apache Iceberg Rust version

None

Describe the bug

The existing implementation of ParquetWriter::current_written_size (link) won't be accurate because it does not take its inner writer's buffer into account, and its self.written_size will only be accurate when closing the parquet writer. A more detailed analysis can be found here

To Reproduce

No response

Expected behavior

We should use inner.bytes_written + inner.in_progress_size to get an estimate size for the current_written_size

Willingness to contribute

I can contribute a fix for this bug independently