GET /v3/instruments/:id/prices

Fetch the full price history for an instrument.

Path params:
  id (required) — Instrument identifier (Mongo ObjectID).

Query params:
  fromDate (optional) — Earliest observation date to include (ISO 8601).
  toDate   (optional) — Latest observation date to include (ISO 8601).

Response (200 OK):
{
  "data": [
    {
      "id": "string",
      "type": "price",
      "attributes": {
        "date":     "ISO 8601 date",
        "value":    "number",
        "provider": "string (e.g. 'client', or a market-data source name)"
      }
    }
  ]
}