Add support for translations.txt to gtfs-schedule module

[Copilot]

This PR adds support for the translations.txt file to the gtfs-schedule module, following the GTFS Schedule reference specification.

Changes

New Model: Translation

Added a new Translation data class representing records in the translations.txt file with all seven fields from the GTFS specification:

• Required fields:

  • tableName - Defines the table containing the field to be translated
  • fieldName - Name of the field to be translated
  • language - Language code for the translation (using LanguageCode type)
  • translation - The translated value

• Optional fields:

  • recordId - Identifies the record containing the field to be translated (first or only field of table's primary key)
  • recordSubId - Additional identifier for tables without unique IDs (second field of table's primary key)
  • fieldValue - Alternative to record identifiers; applies translation when field contains this exact value

Testing

Added comprehensive test coverage in TranslationTest.kt demonstrating all usage patterns:

• Translation using recordId (e.g., translating agency name)
• Translation using recordSubId (e.g., translating stop name with composite key)
• Translation using fieldValue (e.g., translating headsign text)

Documentation

Added translations.txt to the TODO list in ProducerTest.kt for finding sample datasets that publish translation data.

Implementation Notes

The implementation follows all existing patterns in the codebase:

• Uses @Serializable for CSV parsing with kotlinx-serialization
• Proper KDoc comments on all fields
• Consistent with data types used in other models (e.g., LanguageCode from utils)
• All tests pass across all platforms (JVM, JS, Native, WASM)
• API dumps automatically updated
• Zero linting issues

This enables applications using the library to parse and utilize multilingual GTFS datasets that provide translations for customer-facing text.

Original prompt

Please add support for translations.txt to the gtfs-schedule module. Use gtfs.org/documentation/schedule/reference#translationstxt as a reference. Follow all existing patterns, especially the data types used and the tests. Remember to uncomment the relevant lines in producertest when you've added the model, or add it to the list at the bottom if none are available.

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