xpra: 2.5.3 -> 3.0.5

[wamserma]

Motivation for this change

Closes #78707.
Old version (2.5.3) is EOL from upstream.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[leo60228]

I just got a chance to test this, but it seems like (likely due to unrelated changes?) both this and a self-built Xpra hang immediately after opening a socket. strace shows that the hang is on a poll. I have to pkill -9 or ^\, not just ^C.