[READ-ONLY] Mirror of https://github.com/mostlyobvious/En57. DCB-compatible event store library in Ruby with support for PostgreSQL.

Add ActiveRecord adapter master

- Let ActiveRecord hosts share their existing connection pool while the repository continues to execute raw pg queries. - Add the adapter to shared integration and stress coverage so behavior is exercised alongside raw pg and Sequel. - Cover checkout, serializable transaction wrapping, and error propagation with mock-based adapter tests.