GH-49576: [Ruby] Add support for custom metadata in Footer

[kou]

Rationale for this change

In file format, Footer can have custom metadata.

What changes are included in this PR?

• Add garrow_record_batch_file_reader_get_metadata()
• Add garrow_record_batch_file_writer_new_full()
• Add ArrowFormat::FileReader#metadata
• Add metadata to ArrowFormat::FileWriter#finish
• Add metadata: to Arrow::Table#save

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes.

• GitHub Issue: [Ruby] Add support for custom metadata in Footer #49576

[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}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #49576 has been automatically assigned in GitHub to PR creator.

[kou]

+1

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 2 benchmarking runs that have been run so far on merge-commit c24bc29.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 20 possible false positives for unstable benchmarks that are known to sometimes produce them.