[Go] Implement Repeated Reads Solution with request-scoped caching

[davideme]

Task

Implement POST /lamps/bulk-toggle with request-scoped caching to avoid querying the same room multiple times.

Endpoint

POST /lamps/bulk-toggle

{
  "lampIds": ["uuid1", "uuid2", "uuid3"],
  "status": true
}

Functional Requirement

Must not query the same room multiple times even if multiple lamps belong to the same room.

Implementation Hints

• Use a map[uuid.UUID]*Room as request-scoped cache
• Check map before querying database
• Store fetched rooms for reuse within same request
• Pass cache through context or as parameter

Acceptance Criteria

• Bulk toggle updates all specified lamps
• Room validation occurs for each lamp (room must be active)
• Same room is only queried once per request (verify with SQL logging)
• Returns 422 if any lamp belongs to deleted room

Parent Issue

Relates to #289