fix(core): use Rain contract address for price history

[realfishsam]

Summary

• Resolve Rain outcome market ids to on-chain contract addresses before fetching OHLCV.
• Call the Rain SDK getPriceHistory with marketAddress, interval, and option instead of silently ignored marketId/optionIndex/limit keys.
• Add focused regression coverage for both the fetcher parameter contract and exchange-level market-id resolution.

Fixes #1193

Test Plan

• npm test --workspace=pmxt-core -- --runInBand core/test/exchanges/rain-fetcher.test.ts
• npm run build --workspace=pmxt-core

[realfishsam]

Verified in this low-hanging PR automation run: GitHub required checks are green; locally ran npm test --workspace=pmxt-core -- --runInBand core/test/exchanges/rain-fetcher.test.ts (2 tests passed) and npm run build --workspace=pmxt-core (passed).