Unify collection #to_comma extensions

[eitoball]

What

Replace the duplicated #to_comma one-liner on Array, Mongoid::Criteria, and DataMapper::Collection with a shared Comma::CollectionExport module.

Why

Three files implemented the exact same method body. Extracting it into one module removes the duplication without touching ActiveRecord::Relation, which has genuinely different logic (:find_each vs :each selection based on limit/order, plus a warning log) and stays separate.

Fixes #165

Changes

• Add lib/comma/collection_export.rb with Comma::CollectionExport#to_comma
• lib/comma/array.rb, lib/comma/mongoid.rb, lib/comma/data_mapper_collection.rb now include Comma::CollectionExport instead of defining their own to_comma
• Reorder requires in lib/comma.rb so collection_export loads before data_mapper_collection (which includes it eagerly at load time)
• Add lib/comma/collection_export.rb to the Style/Documentation exclude list in .rubocop_todo.yml, matching the existing convention for this project's lib files

No public API change; ActiveRecord::Relation#to_comma is unaffected.

Test plan

• bundle exec rspec — 57 examples, 0 failures
• bundle exec rubocop — no offenses
• Note: spec/comma/rails/mongoid_spec.rb and spec/comma/rails/data_mapper_collection_spec.rb are pre-existing and gated behind if defined? Mongoid/DataMapper; neither gem is a dependency anywhere in this project, so these specs don't execute here or in CI (unrelated to this change)

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The refactor cleanly removes duplication while preserving the existing to_comma behavior and ensures load order correctness via updated requires.

Pull request overview

This PR removes duplicated #to_comma implementations across non-ActiveRecord collection integrations by extracting the shared one-liner into a single Comma::CollectionExport module, keeping ActiveRecord::Relation#to_comma untouched due to its special iterator-selection behavior.

Changes:

• Introduces Comma::CollectionExport#to_comma as the shared implementation.
• Updates Array, Mongoid::Criteria, and DataMapper::Collection extensions to include Comma::CollectionExport instead of redefining to_comma.
• Adjusts lib/comma.rb require ordering so collection_export loads before extensions that include it, and updates RuboCop todo excludes accordingly.

File summaries

File	Description
lib/comma/collection_export.rb	Adds shared to_comma implementation for collection-like types.
lib/comma/array.rb	Replaces inline to_comma with include Comma::CollectionExport.
lib/comma/mongoid.rb	Replaces inline to_comma with include Comma::CollectionExport for Mongoid criteria.
lib/comma/data_mapper_collection.rb	Replaces inline to_comma with include Comma::CollectionExport for DataMapper collections.
lib/comma.rb	Requires collection_export before extensions that depend on it.
.rubocop_todo.yml	Excludes new lib file from Style/Documentation to match existing project pattern.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 0
• Review effort level: Lite

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