Refactor FlightPhases and Optimize Test Suite TestFlightPhases

[JaskRendix]

Summary of changes:

• replaced namedtuple with @dataclass for the Phase structure to improve readability and extensibility
• expanded Phase to include metadata fields such as duration, altitude_gain, average_climb_rate and timestamps (start_time, end_time)
• added type annotations throughout the codebase for better clarity and static analysis
• improved leg handling logic with safer type checks and more robust validation
• switched to f-strings for cleaner and more modern string formatting
• centralized TestFlightPhases setup using setUpClass to eliminate redundant initialization and improve maintainability
• reduced test suite runtime from ~14 seconds to ~7 seconds
• ran isort across the project to standardize and clean up import ordering
• added filter_by_time_range() and filter_by_location() methods to FlightPhases for segmenting phases by temporal or geographic criteria
• added summary_stats() method to FlightPhases to compute aggregate metrics such as total thermals/cruises, average thermal duration and total cruise distance