enable to-nu to include the whole dfr if rows is not specified

[fdncred]

Description

Before this PR, to-nu would only return 5 rows if rows was not specified. This PR changes that to allow to-nu to return the entire dfr unless rows is specified.

closed #4752

Tests

Make sure you've run and fixed any issues with these commands:

• cargo fmt --all -- --check to check standard code formatting (cargo fmt --all applies these changes)
• cargo clippy --all --all-features -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect to check that you're using the standard code style
• cargo build; cargo test --all --all-features to check that all the tests pass