Fix building on modern nixpkgs/for python3.13

[mazunki]

nix-build doesn't work because future doesn't exist for python3.13 in current nixpkgs.

This PR allows us to compile. It also cleans up some python2.7 legacy, and fixes shebangs.

[mazunki]

Running phase: installCheckPhase
Checking vmrunner/bin/create_bridge.sh with shellcheck
Checking vmrunner/bin/create_memdisk.sh with shellcheck
Checking vmrunner/bin/grubify.sh with shellcheck
Checking vmrunner/bin/solo5-ifup.sh with shellcheck
Checking vmrunner/bin/qemu-ifup with shellcheck
Checking vmrunner/bin/qemu-ifdown with shellcheck
Checking vmrunner/__init__.py with pylint
copying path '/nix/store/wb7icc6mcfns22r9pk7psmr25s02c0lq-libadwaita-1.7.6' from 'https://cache.nixos.org'...
copying path '/nix/store/lqzs8p1ffzc58mjwh5g7dabjznqj49ma-zenity-4.1.90' from 'https://cache.nixos.org'...
Checking vmrunner/boot.py with pylint
copying path '/nix/store/6vwg93gfcwblqg78934qa6wkapd16a5j-sdl3-3.2.20-lib' from 'https://cache.nixos.org'...
copying path '/nix/store/6my8jb7kcqd4xinvmgiqvpmhc273mczq-sdl2-compat-2.32.56' from 'https://cache.nixos.org'...
copying path '/nix/store/8yjzcnrwavih44jzfva8ksfcbwyfphjl-SDL2_image-2.8.8' from 'https://cache.nixos.org'...
copying path '/nix/store/yd1rlziy0cnjjp78zc7wr9dcv5hah16w-qemu-10.1.0' from 'https://cache.nixos.org'...

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Checking vmrunner/prettify.py with pylint

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Checking vmrunner/validate_vm.py with pylint

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Checking vmrunner/vmrunner.py with pylint

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[mazunki]

I'm trying to find a reference for the lack of spaces between shebang and interpreter path. Best I can find is this:
https://homepages.cwi.nl/~aeb/std/shebang/

Either way, pretty much every recommendation you see around does /not/ use a space. Deviating from the convention makes it harder to grep for these things.

Seems like it's actually unspecified, but works on basically all implementations: https://www.in-ulm.de/~mascheck/various/shebang/#blankrequired