fix: expose market data provider to executors

[matvt-cell]

Summary

Companion change for hummingbot/hummingbot#8453 and hummingbot/hummingbot#8437.

Hummingbot API already uses MarketDataService as its pricing source, but executor strategies did not expose that service through the market_data_provider interface expected by the core GridExecutor fee-conversion path.

This change exposes the existing MarketDataService from AccountTradingInterface as market_data_provider.

That allows GridExecutor in hummingbot/hummingbot#8453 to resolve third-token fees such as BNB -> USDT through the API market-data pricing pool instead of relying exclusively on the legacy RateOracle singleton.

Changes

• add AccountTradingInterface.market_data_provider
• return the existing _market_data_service
• add a focused regression test verifying the same provider instance is exposed

Tests

python -m pytest test/test_account_trading_interface.py -q

1 passed

Dependency

Depends on hummingbot/hummingbot#8453

Related to hummingbot/hummingbot#8437

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with no concrete changed-code failure established.

Summary

• Adds a read-only provider property to the executor-facing trading interface.
• Adds a regression test confirming that the property returns the same injected service instance.

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