Refactor duplicated code patterns in NetTool

[Copilot]

Eliminated 100+ lines of duplicated Winsock initialization, command-line parsing, and error handling code across the NetTool directory.

Changes

Created shared utilities (common_utils.h/cpp):

• WinsockInitializer - RAII class for automatic Winsock lifecycle management
• getopt() - BSD-style command-line parsing
• Error handling functions: err(), errx(), verr(), verrx()

Refactored 6 files to use shared utilities:

• finger.cpp - Removed ~130 lines (getopt impl, error functions, Winsock boilerplate)
• whois.cpp, Ping.cpp, nslookup.cpp - Replaced manual Winsock init/cleanup with RAII
• sock.cpp - Applied RAII to 5 functions

Fixed resource leaks:

• Added missing closesocket(s6) calls in 4 functions

Example

Before:

WSADATA wsaData;
int err = WSAStartup(MAKEWORD(1, 1), &wsaData);
if (err != 0) {
    fprintf(stderr, "WSAStartup failed\n");
    return;
}
// ... use sockets ...
WSACleanup();

After:

WinsockInitializer winsock(MAKEWORD(1, 1));
if (!winsock.IsInitialized()) {
    fprintf(stderr, "WSAStartup failed\n");
    return;
}
// ... use sockets ...
// Automatic cleanup on scope exit

Original prompt

Find and refactor duplicated code

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