Check installer permissions using geteuid

Hi!
I noticed EBPF doesn't correctly check the permission whether the user has root privilege or not. Instead, it relies on other functions' errors. (E.g. In libsysinternalsEBPFinstaller.c at line 279, it relies on mkdir(...) and stat(...) functions' success/errors). It would be better to just check the permission through geteuid(...) instead.

if (geteuid() != (uid_t)0) {
     // Error message
}

Something like this also fixes an issue where with the -u flag (uninstall), the installer (libsysinternalsEBPFinstaller.c) doesn't check the permission at all.

Start in libsysinternalsEBPFinstaller.c around line 279 and trace both the normal installation path and the -u uninstall path. Check how the current mkdir/stat errors are used for permission handling, then verify that both paths reject users whose geteuid is not zero with an appropriate error message.