(CVE-2025-5024) Add connection throttling

Jonas Ådahlrequested to merge
jadahl/gnome-remote-desktop:wip/throttle into main

From the commit that introduces the throttler:

  • It limits the global number of concurrent active connections
  • It limits the number of concurrent active connections per peer (roughly IP address)
  • It limits the number of new connections per second coming from a peer
  • It maintains a limited number of pending connections that is waiting to be handled

Mitigates CVE-2025-5024.

There is also a commit that avoids incorrect closing of file descriptors.

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