feat: completion of Atomic reservation and order life cycle

[codewithme-py]

Atomicity of the database: Implemented strict transactional blocking SELECT ... FOR UPDATE in inventory and order services to prevent Race Conditions for parallel purchases.

Protection against DDoS and spam: Integrated Dual-Layer Lua Rate Limiter and decorator @idempotent (via Redis) to protect key endpoints for booking and order creation.

Orders API: A router with full-cycle endpoints has been added:

• POST /orders/ (Creating an order from the reservation)

• POST /orders/{id}/pay (Successful payment -> write-off of goods)

• POST /orders/{id}/cancel (Cancel -> return of goods to the warehouse)

Migrations: Updated database types and schemes (removed Nullable from the product price, added status COMPLETED in OrderStatus
Type security: Refactoring of models and Pydantic schemes was carried out. The code completely passes the strict checks of mypy and ruff.

The logic of API responses has been improved: transition from unconditional 404 to 409 Conflict when trying to change the inappropriate order status.