Fix ArrayHandlerPatch to support multi-database configurations

[biancapower]

Problem

ArrayHandlerPatch#call hardcodes ActiveRecord::Base.connection to check the schema cache for PostgreSQL array columns. In Rails 6.1+ multi-database setups where connects_to is declared on abstract subclasses (not ActiveRecord::Base itself), ActiveRecord::Base has no connection pool registered. This raises ActiveRecord::ConnectionNotDefined on any .where() with array values.

Minimal reproduction:

class ApplicationRecord < ActiveRecord::Base
  primary_abstract_class
  connects_to database: { writing: :primary, reading: :primary_replica }
end

# Any model with an array column:
Role.where(name: ["admin", "doctor"])
# => ActiveRecord::ConnectionNotDefined: No database connection defined.

Fix

Resolve the connection through the model that owns the Arel table, via attribute.relation. Arel::Table stores the owning model as @klass (set via the klass: keyword argument in its constructor). There is no public accessor,
so we use instance_variable_get(:@klass) with a fallback to ActiveRecord::Base for cases where klass is nil (e.g. hand-built Arel tables).

This is the minimal change — the rest of the method is untouched.

Notes

• Verified on Rails 8.0.3 with PostgreSQL and a multi-database config (separate primary + queue databases)
• The fallback to ActiveRecord::Base preserves existing behavior for single-database setups
• @klass has been present on Arel::Table since Rails 5.2 and is used internally by Rails for attribute alias resolution