Fix ArgumentError sorting unnamed foreign keys when one is composite

[6temes]

Fixes #377

Problem

ForeignKeyComponentBuilder#formatted_name falls back to the raw foreign_key.column when a foreign key has no name. On adapters that report unnamed foreign keys (SQLite reports all of them that way), a composite foreign key yields an Array while ordinary ones yield a String, and AnnotationBuilder#build's sort_by { |fk| [fk.formatted_name, fk.stringified_columns] } raises ArgumentError: comparison of Array with Array failed. In a Rails app this makes every db:migrate/db:rollback exit non-zero after the migration completes, since the rake hook runs afterwards.

Fix

Use the existing stringified_columns as the no-name fallback, so the sort key and the rendered name are always Strings. For a composite key that renders as [delivery_on, menu_id], matching the style ref_info already uses. This also makes the max_size padding measure the rendered width instead of Array#size.

Verification

• New spec (unnamed simple + unnamed composite key on one model) reproduces the exact ArgumentError without the fix and passes with it.
• Full suite failure count is unchanged versus main in my environment (the same 26 pre-existing failures on both, unrelated to this change).