GH-49389: [Ruby] Add support for custom metadata in field and schema

[kou]

Rationale for this change

We can add custom metadata to Field and Schema.

What changes are included in this PR?

• Add ArrowFormat::Field#metadata
• Add ArrowFormat::Schema#metadata
• Add support for reading and writing custom metadata in Field and Schema

Are these changes tested?

Yes.

Are there any user-facing changes?

Yes.

• GitHub Issue: [Ruby] Add support for custom metadata in field and schema #49389

[github-actions]

⚠️ GitHub issue #49389 has been automatically assigned in GitHub to PR creator.

[hiroyuki-sato]

+1

LD_LIBRARY_PATH=/tmp/local/lib:/path/to/arrow/red-arrow/ext/arrow/ GI_TYPELIB_PATH=/tmp/local/lib/girepository-1.0 rake -I /path/to/arrow/ruby/red-arrow/lib test
cd /path/to/arrow/ruby/red-arrow-format
/path/to/.rbenv/versions/3.4.7/bin/ruby test/run.rb
Loaded suite test
Started
/path/to/arrow/ruby/red-arrow-format/lib/arrow-format/file-reader.rb:41: warning: IO::Buffer is experimental and both the Ruby and C interface may change in the future!
Finished in 3.256675261 seconds.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
292 tests, 292 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
100% passed
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
89.66 tests/s, 89.66 assertions/s
cd -

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit dc5b76e.

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.