Unify collection #to_comma extensions

[eitoball]

Summary

Replace duplicated #to_comma implementations on Array, Mongoid::Criteria, and DataMapper::Collection with a shared module.

Problem

Three files implement the same one-liner pattern:

def to_comma(style = :default)
  Comma::Generator.new(self, style).run(:each)
end

Locations:

• lib/comma/array.rb
• lib/comma/mongoid.rb
• lib/comma/data_mapper_collection.rb

ActiveRecord::Relation (lib/comma/relation.rb) is different — it chooses :find_each vs :each based on limit/order and logs a warning. That logic should stay separate.

Proposed approach

# lib/comma/collection_export.rb
module Comma
  module CollectionExport
    def to_comma(style = :default, iterator: :each)
      Comma::Generator.new(self, style).run(iterator)
    end
  end
end

Then:

class Array
  include Comma::CollectionExport
end

Same for Mongoid and DataMapper hooks.

Files likely involved

• New: lib/comma/collection_export.rb
• lib/comma/array.rb
• lib/comma/mongoid.rb
• lib/comma/data_mapper_collection.rb
• lib/comma.rb (require new file)
• Existing collection specs (comma_spec, mongoid_spec, data_mapper_collection_spec)

Acceptance criteria

• Array#to_comma, Mongoid criteria, and DataMapper collection behavior unchanged
• ActiveRecord::Relation#to_comma unchanged (still uses custom iterator)
• No public API change
• Duplicated #to_comma bodies removed from three files

Labels (suggested)

refactor, good first issue

Depends on

None.