Add anonymized benchmark SQL imports to MariaDB CI

[oppiet30]

Summary

• Copy four existing benchmark SQL imports into tests/fixtures/benchmark-imports/ without changing the originals.
• Rename only the machine hostnames in the copies to test1, test2, test3, and test4.
• Seed the matching datasets/models in the disposable CI schema.
• Import the four fixture files into GitHub Actions' temporary MariaDB instance and assert that four benchmark rows were imported for the anonymized hosts.

Safety

• The workflow uses a disposable MariaDB 11.8 service; it does not connect to a developer's database.
• Original benchmark SQL files remain unchanged.
• This PR does not contain credentials or local connection configuration.

Validation

GitHub Actions will run on this PR. The fixture import step explicitly checks that exactly four benchmark runs were imported.