Refactor and code cleanup

[tkjaer]

Summary

This PR introduces cleanups across the codebase and refactors code for readability.

Details

Program flow and signal handling:

• Refactored main.go to move program logic into a run() function, improving signal handling for interrupts (Ctrl+C). Now, the program exits gracefully on the first interrupt and immediately on a second interrupt. This also simplifies error handling and resource cleanup. [1] [2] [3]
• Improved the shutdown sequence by extracting logic into a new waitForCompletion function and using a sentinel error for forced exit.

Argument parsing and CLI improvements:

• Reorganized and grouped CLI flags in ParseArgs for better usability, added missing short flags in help examples, and ensured the help text matches the actual flags. [1] [2]

ICMP probe decoding and packet handling:

• Refactored ICMPv4 and ICMPv6 probe decoding logic for clarity and correctness: replaced nested and repetitive code with helper methods, improved error handling for truncated packets, and consolidated IP/port matching logic. [1] [2] [3]
• Added a helper method innerIPsMatch to centralize IP address validation in decoded packets.
• Improved extraction of metadata (network layer and timestamp) in packet decoding.

Code clarity and cleanup:

• Removed excessive debug logging from ARP table lookup code on BSD systems for cleaner logs. [1] [2]
• Removed unused or commented-out code related to statistics aggregation and summary generation in ProbeManager. [1] [2]
• Minor variable renaming for consistency (e.g., ttl_exceeded to ttlExceeded) in BPF filter setup. [1] [2]

Bug fixes and minor improvements:

• Fixed integer overflow bug in infinite probe count assignment.
• Added clarifying comments and minor documentation improvements in shared types.
• Improved comments in probe run output to clarify timestamp handling.