Close all owned module sessions in PerpetualTradingClient.close()

[vikions]

Summary

• close the missing info, vault, and testnet module sessions in PerpetualTradingClient.close()
• add a regression test that opens a session through every public sub-client and verifies they are closed after close()

Why

PerpetualTradingClient creates six module clients, but close() only cleaned up three of them. If a caller used client.info, client.vault, or client.testnet, their underlying aiohttp sessions could stay open and leak resources.

Testing

• python -m py_compile x10/perpetual/trading_client/trading_client.py tests/perpetual/test_trading_client.py
• pytest tests/perpetual/test_trading_client.py -k close_closes_all_module_sessions
  not runnable in my local environment because hamcrest is not installed