Use CoinGecko for KuCoin futures top movers

[carkod]

Motivation

• KuCoin futures per-contract 24h percentage change is not available from the existing KuCoin/spot endpoints used for charts, so a reliable discovery/ranking source is needed for top-gainers/top-losers.

Description

• Added CoinGecko.get_kucoin_futures_tickers() which calls GET /derivatives/exchanges/kumex?include_tickers=unexpired and returns per-contract tickers.
• Wired a CoinGecko client into MarketDominationController and replaced the previous Binance/spot-based ranking with filtering for USDT perpetual KuCoin futures and sorting by h24_percentage_change.
• Updated chart endpoints tests in api/tests/test_charts.py to monkeypatch CoinGecko.get_kucoin_futures_tickers and assert the top-gainers/top-losers payloads, and added a controller-level test in test_market_domination_controller.py to exercise filtering and ordering logic.
• Added request timeouts (10s) to CoinGecko client calls for better network resilience.

Testing

• Ran code formatting with make format and fixes were applied with no issues.
• Ran the test suite with env ... make test (test environment variables provided) and the full test run completed successfully with all tests passing (120 passed).

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Codex Task