arrow

GH-39789: [Go][Parquet] Close current row group when finished writing unbuffered batch (#43326)



### Rationale for this change

Fixes: #39789

The number of bytes reported by `FileWriter.RowGroupTotalBytesWritten()` was consistently lower than the actual bytes in the output buffer, if it was read before closing the writer. The issue is that the last column's data page was not flushed until the entire writer was closed, causing it's bytes not to be included in the total. By closing the row group writer before returning from `Write()`, we can ensure all pages are flushed and the totalBytesWritten will be accurate.

### What changes are included in this PR?

- Close row group writer before returning from `FileWriter.Write()`
- Test to ensure stats are up to date _before_ closing the writer

### Are these changes tested?

Yes

### Are there any user-facing changes?

`FileWriter.RowGroupTotalBytesWritten()` will be accurate when read while still writing to the file.

* GitHub Issue: #39789

Authored-by: Joel Lubinitsky <joellubi@gmail.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>