Write null counts in Parquet statistics when they are known to be zero

[alamb]

Describe the bug
The Rust parquet writer writes the thrift equivalent of None when the null count is zero rather than the thrift equivalent of Some(0)

This is inconsistent with the spec and other major implementations (Java and C++)

To Reproduce

Expected behavior
Write Some(0) when null count is known to be zero

Additional context
Part of #6256, but we split out the read/write changes into smaller PRs so adding a special issue here to track it / show up in the release notes

[alamb]

Fixed by @etseidl in #6490