Refactor command-line argument parsing

[tgrothe]

Refactor command-line argument parsing

closes #5

This pull request refactors and enhances the argument parsing and execution logic for the port knocking tool in Main.java. The changes introduce a finite state machine (FSM) for argument validation, improve input parsing, and restructure the knocking sequence to use a list of actions. Additionally, output messages are improved for clarity.

Argument parsing and validation improvements:

• Replaced the previous mode-based parsing with a finite state machine (fsm) using a Symbol enum and a Map to enforce valid argument sequences and transitions. [1] [2] [3]
• Added helper methods parseDelay and parsePort to validate and parse delay and port arguments, ensuring values are within acceptable ranges.

Knocking sequence execution changes:

• Changed the knocking sequence to a list of Runnable actions, allowing flexible sequencing of UDP/TCP knocks and delays, and removed the last delay to avoid unnecessary waiting. [1] [2]
• Added a new knockDelay method to encapsulate delay logic and handle interruptions gracefully.

Output and feedback enhancements:

• Updated knockUDP and knockTCP methods to print status messages before and after each knock, providing better user feedback. [1] [2]