Refactor the service layer

[BytecodeBrewer]

Goal

Clean up legacy service structure after introducing MarketDataService.

Why

Some early services were created when ARGUS was still a smaller FX/converter project. As ARGUS moves toward market data, analytics and reporting, these services should be simplified or removed.

Scope

• Mark calculator_service as legacy or remove i
• Remove calculator-related tests
• Dissolve conversion_service
• Move small pure conversion logic into the domain layer where useful
• Remove outdated tests or update them to match the new structure

Acceptance criteria

• calculator_service is marked as legacy or removed
• Calculator-related tests are removed
• conversion_service is dissolved
• Pure conversion logic is moved into the domain layer where useful
• Outdated tests are removed or updated

Note

Priority: Should