Add ICE Brent Futures endpoints

[karlwaldman]

Overview

Add support for ICE Brent futures data endpoints (Premium feature).

Endpoints to Add

• GET /v1/futures/ice-brent - Get ICE Brent futures curve
• GET /v1/futures/ice-brent/historical - Get historical futures data with optional contract_month and period params
• GET /v1/futures/ice-brent/spreads - Get calendar spreads between contract months

Types Needed

• BrentFuturesResponse
• BrentFuturesHistoricalOptions
• FuturesSpreadsResponse

Priority

P1 - High Value - Requested by Reservoir Mastery tier users

Swagger Reference

See swagger/v1/swagger.json in oilpriceapi-api repo for schema details