Support opt-in display of PostgreSQL enum types in annotations

[OdenTakashi]

Summary

This change adds an opt-in show_enums option for PostgreSQL model annotations.

When enabled, it:

• adds an enum_type: attribute to enum columns
• adds an Enums section below the schema
• lists only the enum types used by the table

This feature is supported only for PostgreSQL and is safely skipped for MySQL and SQLite.

connection.enum_types was introduced in Rails 7.0 (rails/rails#41469) and may return either a String or an Array depending on the Rails version (rails/rails#54141). This gem handles both formats.

Return type	Rails versions
String (string_agg)	Rails 7.0 - 8.0.1
Array (array_agg)	Rails 7.2.3+, 8.0.2+

Example

Output follows the format proposed in #176.

# == Schema Information
#
# Table name: orders
#
#  id      :bigint           not null, primary key
#  status  :enum             not null, enum_type: order_status
#  billing :enum             enum_type: billing_method
#
# Enums
#
#  billing_method  agency_bill, direct_bill_to_insured
#  order_status    pending, shipped, delivered
#

Configuration

# .annotaterb.yml
show_enums: true

refs: #176 , #309