fix: Prevent crash in packet::parse by validating std::stoi input

[JeHeeYu]

This PR addresses an issue where std::stoi would throw an std::invalid_argument exception when the Socket.IO packet payload contained non-numeric characters in the expected pack ID field.

Changes include:

• Added validation to check whether the substring is numeric before calling std::stoi.
• Added logging for malformed packet segments to aid debugging.
• Ensures stability when binary or malformed packets are received.

This change prevents application crashes caused by invalid Socket.IO payloads, particularly under Linux, where behavior previously diverged from Windows.

[jmigual]

Thanks for your work!