security: unnecessary requirement for persistent root privilege for MSR

Current Problem:

Current XMRig documentation and internal messaging encourages users to run the entire process with root privileges. This is an unnecessary security risk because the requirement for root is transient, yet the application remains as root for its entire lifecycle.

From https://xmrig.com/docs/miner/randomx-optimization-guide/msr:

If you use recent XMRig with root privileges (Linux) or admin privileges (Windows) the miner configure all MSR registers automatically.

As far as I'm aware this is the only reason to run XMRig as root.

By suggesting users run XMRig with elevated privileges, the project is advocating a violation of the principle of least privilege. When running XMRig as root it risks system compromise if a vulnerability is found in the Stratum protocol handling, HTTP API, or JSON-RPC components. It is a major unnecessary risk.

Proposed solution:

I believe that in terms of UX, the best way to solve this problem would be to have the MSR modification as a separate program/process. Though, I believe this is unlikely to be done as it would break past behaviour. Instead, the most realistic approach I see to solving this is XMRig adding a --user flag. If started as root then XMRig should perform the MSR setup then immediately drop to the specified unprivileged user using setuid/setgid. To avoid breaking things for now I believe there should be a warning to the user when XMRig is run with CAP_SYS_ADMIN without providing an argument to --user. As many other programs do, running as root should be allowed, but discouraged.