Functionalities to accept no spam request sessions

[SnowCheetos]

• Implemented the ability to accept session as an init argument to AlphaVantage to allow no-spam request sessions.
• Added session instance type checker to make sure that a valid type is used, otherwise default to None.
• Modified AlphaVantage._handle_api_call to use the request session if it is available.
• Added tests for the session request functionalities.
• Confirmed that original methods of AlphaVantage functions properly with the modifications.
• Commented out tests for sector_performance since the method doesn't exist anymore.