feat: support direct credentials in TradingSuite.create

[rupurt]

Summary

• allow TradingSuite.create to accept direct ProjectX username/api_key credentials
• forward account_name to direct or environment-backed client creation instead of TradingSuiteConfig
• add regression coverage for direct credentials and partial credential validation

Why

TradingSuite.create accepted arbitrary kwargs for suite configuration and always created its ProjectX client with ProjectX.from_env(). Callers that supplied username, api_key, or account_name had those values forwarded into TradingSuiteConfig, causing an unexpected keyword argument failure before market data could initialize.

Validation

• uv run pytest tests/trading_suite/test_core.py -q
• uv run ruff check src/project_x_py/trading_suite.py tests/trading_suite/test_core.py
• uv run ruff format --check src/project_x_py/trading_suite.py tests/trading_suite/test_core.py