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GH-38516: [Go][Parquet] Increment the number of rows written when appending a new row group (#38517)

### Rationale for this change

This makes it so the `NumRows` method on the `file.Writer` reports the total number of rows written across multiple row groups.

### Are these changes tested?

A regression test is added that asserts that the total number of rows written matches expectations.

* Closes: #38516

Authored-by: Tim Schaub <tim@planet.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>