feat(importers): MySQL/MariaDB importer wire & verify (v1.8.0)

[Copilot]

Wires mysql_importer.cpp into the IImporterPluginRegistry via static-init self-registration and exposes it through the admin import API as POST /api/v1/import/mysql.

Core Changes

Registry Registration (mysql_importer.h / mysql_importer.cpp)

• Added MySQLImporterSchemePlugin : public IImporterPlugin handling mysql:// and mariadb:// URI schemes
• Registered at static-init time via REGISTER_IMPORTER_PLUGIN — no manual wiring required:

// src/importers/mysql_importer.cpp (bottom)
namespace themis {
namespace importers {
REGISTER_IMPORTER_PLUGIN(MySQLImporterSchemePlugin)  // wraps in namespace to keep ## token-paste valid
} // namespace importers
} // namespace themis

Bug fixed: The initial attempt used REGISTER_IMPORTER_PLUGIN(themis::importers::MySQLImporterSchemePlugin) at global scope, which causes a compile error — the ## token-paste in the macro produces invalid identifiers containing ::.

Admin Import API (import_api_handler.h / .cpp)

• Added POST /api/v1/import/mysql route → handleStartMySQLImport()
• Handler resolves MySQLImporterSchemePlugin from IImporterPluginRegistry::instance() at request time; returns 501 if the plugin is absent, 400 for missing source_path
• importer_interfaces.h added to import_api_handler.h includes for IImporterPluginRegistry / ImportConfig visibility

Already Satisfied ACs (no changes needed)

• Prometheus counters importers_mysql_rows_imported_total / importers_mysql_errors_total already emitted in importData() (lines 278, 281, 874, 888)
• Docker MySQL 8.0 integration test already present as mysql-live-integration job in importer-tests.yml

Testing

• Unit tests added/updated — tests/test_mysql_importer_registry.cpp: 12 tests covering mysql:///mariadb:// scheme resolution, createImporter() instance isolation, plugin-id list membership, and admin route guard logic
• Integration tests added/updated — mysql-live-integration CI job (pre-existing): seeds MySQL 8.0 Docker container, dumps with mysqldump, exercises the full importer pipeline
• Manual testing performed

New Test Infrastructure

• tests/mysql_importer_registry_logger_stub.cpp — no-op Logger stub so the registry test binary can link mysql_importer.cpp without the full spdlog chain (mirrors kafka_importer_logger_stub.cpp)
• tests/CMakeLists.txt — standalone test_mysql_importer_registry target + exclude pattern to prevent duplicate extern "C" plugin symbols in the main themis_tests binary

📚 Research & Knowledge (wenn applicable)

• Diese PR basiert auf wissenschaftlichen Paper(s) oder Best Practices?
  • Falls JA: Research-Dateien in /docs/research/ angelegt?
  • Falls JA: Im Modul-README unter "Wissenschaftliche Grundlagen" verlinkt?
  • Falls JA: In /docs/research/implementation_influence/ eingetragen?

Relevante Quellen:

• Paper:
• Best Practice:
• Architecture Decision:

Checklist

• Code follows project style guidelines
• Self-review completed
• Documentation updated (if needed)
• No new warnings introduced

Original prompt

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This section details on the original issue you should resolve

<issue_title>MySQL / MariaDB Importer (wire & verify)</issue_title>
<issue_description>### Context

This issue implements the roadmap item 'MySQL / MariaDB Importer (wire & verify)' for the importers domain. It is sourced from the consolidated roadmap under 🟠 High Priority — Near-term (v1.5.0 – v1.8.0) and targets milestone v1.8.0.

Primary detail section: MySQL / MariaDB Importer

Goal

Deliver the scoped changes for MySQL / MariaDB Importer (wire & verify) in src/importers/ and complete the linked detail section in a release-ready state for v1.8.0.

Detailed Scope

MySQL / MariaDB Importer

Priority: High
Target Version: v1.8.0
Status: src/importers/mysql_importer.cpp exists but needs verification that it is fully wired.

Implementation Notes:

• [ ] Verify mysql_importer.cpp registers with ImporterRegistry and is reachable from the admin import API.
• [ ] Add Prometheus counters importers_mysql_rows_imported_total and importers_mysql_errors_total consistent with other importer naming.
• [ ] Add integration test using a Docker MySQL 8.0 container.

Acceptance Criteria

• Verify mysql_importer.cpp registers with ImporterRegistry and is reachable from the admin import API.
• Add Prometheus counters importers_mysql_rows_imported_total and importers_mysql_errors_total consistent with other importer naming.
• Add integration test using a Docker MySQL 8.0 container.

Relationships

• Roadmap row: Correct AQL language scope documentation and integrate FunctionRegistry to activate 140+ functions #68 (🟠 High Priority — Near-term (v1.5.0 – v1.8.0))
• Depends on: none identified during generation.
• Part of: consolidated roadmap delivery tracking.

References

• src/ROADMAP.md
• src/importers/FUTURE_ENHANCEMENTS.md#mysql--mariadb-importer
• Source key: roadmap:68:importers:v1.8.0:mysql-mariadb-importer

Generated from the consolidated source roadmap. Keep the roadmap and issue in sync when scope changes.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes MySQL / MariaDB Importer (wire & verify) #3896

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