Refactor validation service

[laritakr]

Summary

This PR integrates the upstream refactor/validation-lambdas branch into bulkrax-v2-importer, eliminating the ~3,200-line CsvValidationService namespace that re-implemented CSV parsing, column resolution, field mapping, and row categorization already handled by CsvParser and CsvEntry. Validation and template generation are now concerns on CsvParser itself, backed by focused service classes and callable validator modules.

Changes

Architecture

• CsvParser::CsvValidation concern — all validation logic lives here, using CsvParser.validate_csv as the single entry point. Uses CsvEntry.read_data (not CSV.read) to preserve blank-row filtering identical to a real import.
• CsvParser::CsvTemplateGeneration concern — template generation extracted cleanly, with a nested TemplateContext class wiring the CsvTemplate::* components
• Bulkrax::CsvRow::* validators — 4 callable modules in app/validators/ (DuplicateIdentifier, ParentReference, RequiredValues, ControlledVocabulary), each implementing self.call(record, row_number, context)
• Bulkrax::CsvTemplate::* — template sub-components re-namespaced from CsvValidationService:: to CsvTemplate::, with no logic changes
• Bulkrax.config — validators now configurable via csv_row_validators / register_csv_row_validator
• GuidedImportsController — replaces the old GuidedImport controller concern; routes updated accordingly
• docs/ — CSV_SERVICE_ARCHITECTURE.md rewritten, STEPPER_IMPLEMENTATION.md updated to reflect current architecture

Deleted

• CsvValidationService facade and all duplicative sub-components (CsvParser, ColumnResolver, ItemExtractor, Validator, RowValidatorService + 5 sub-validators, MappingManager)
• row_validator_service config accessor (replaced by csv_row_validators)
• All corresponding specs under spec/services/bulkrax/csv_validation_service/

Preserved

• Validation result hash shape (guided import UI compatibility — no frontend changes required)
• Template generation functionality (logic untouched, namespace moved)
• I18n keys for all error and validation messages
• Extensibility — host apps configure validators via:

  Bulkrax.config do |c|
    c.register_csv_row_validator(MyApp::CustomValidator)
  end

Notes

Built extensively on prior PR #1152

We used the upstream PR code directly for:

• All 12 CsvTemplate::* service classes
• CsvParser::CsvTemplateGeneration concern
• CsvParser::CsvValidation concern
• All 4 CsvRow::* validator modules
• Bulkrax.csv_row_validators config
• Controller updates (GuidedImportsController, ImportersController)
• All 12 csv_template/ specs
• The 3 CsvRow validator specs (we initially wrote our own, then replaced them with the upstream versions)
• model_stubbing_helpers.rb

We diverged from upstream in cases where it missed something or was wrong:

• CsvEntry.read_data instead of CSV.read — upstream used CSV.read, which would have broken blank-row filtering. We caught this from the existing e2e specs.
• csv_parser_template_spec.rb — upstream had this spec but it wasn't in the PR; we wrote it matching the upstream version once we identified it was missing
• model_loader_spec.rb — missing entirely from upstream; we wrote it and also fixed the underlying bug in load_models
• controlled_vocabulary_spec.rb — not in the upstream PR at all; we wrote it ourselves
• docs/ — upstream left the docs referencing the old architecture; we rewrote them to reflect the current state
• ModelLoader#safe_constantize — bug fix we added that upstream didn't have