Hook execve and execv to allow shared sockets.

[meowjesty]

• Issue: TCP Steal/mirror doesn't work with shared sockets #864

We now share the SOCKETS created by the parent process with its children (yay happy family) through an env var MIRRORD_SHARED_SOCKETS (the creativity is astonishing) that is set up in exec* calls (and also posix_spawn for macos). The SOCKETS are rebuilt from this env var (if it exists) in the child process.

• Adds a new hook execv for linux;
  • Sets an env var with Rust's set_var;
• Makes the previously macos only execve hook also available on linux;
  • Changes execve behaviour to insert a new env var before calling FN_EXECVE;
• Adds a new integration test for an uvicorn app with the --reload flag, which triggers the issue;

[DmitryDodzin]

Minor changes regarding sip but looks good otherwise =]

[DmitryDodzin]

🥷