GH-38602: [R] Add missing prod for summarize

[m-muecke]

Rationale for this change

prod is currently missing for use in summarize.

What changes are included in this PR?

Added prod for summarize aggregation.

Are these changes tested?

Yes, included the same tests used for the other aggregation functions for summarize.

Are there any user-facing changes?

Yes, added prod function.

• Closes: [R] Implement missing prod function for summarize #38602

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

In the case of PARQUET issues on JIRA the title also supports:

PARQUET-${JIRA_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - How to contribute patches

[github-actions]

⚠️ GitHub issue #38602 has been automatically assigned in GitHub to PR creator.

[paleolimbot]

Very clean! Thank you!

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 5 benchmarking runs that have been run so far on merge-commit 6dcba93.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 1 possible false positive for unstable benchmarks that are known to sometimes produce them.