Improve Red Arrow Active Record integration

[kou]

Fix GH-21

Reported by Dmytro Piliugin. Thanks!!!

[Copilot]

Pull request overview

This PR fixes GH-21 by improving interoperability between activerecord-adbc-adapter and Red Arrow Active Record, ensuring to_arrow / each_record_batch work correctly for both ADBC-backed models and “normal” ActiveRecord adapter-backed models in the same test run.

Changes:

• Add Red Arrow Active Record as a runtime dependency and load it so non-ADBC relations can use the upstream implementations.
• Update relation Arrow conversion methods to use the ADBC-specific path only for this adapter and fall back to super otherwise.
• Extend the test harness to establish a secondary “raw” ActiveRecord connection (SQLite3/PostgreSQL) and add coverage for batching behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lib/activerecord_adbc_adapter/relation_arrowable.rb	Adds Red Arrow Active Record require and routes to_arrow / each_record_batch to ADBC implementation vs super based on adapter class.
test/helper.rb	Establishes an additional non-ADBC AR connection for RawUser to validate Red Arrow Active Record behavior; adjusts DB creation config for PostgreSQL.
test/helper/user.rb	Introduces RawUser mapped to the same users table without ADBC ingest mixin.
test/test_model.rb	Adds/updates tests to cover Red Arrow Active Record batching (batch_size) and record batch enumeration.
Gemfile	Adds sqlite3 for test runs that use the raw ActiveRecord SQLite3 adapter.
activerecord-adbc-adapter.gemspec	Adds runtime dependency on red-arrow-activerecord (>= 0.1.4).

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