nixos/terraria: fix service restarting and refactor to use config file

[TomaSajt]

Description of changes

This PR revamps the services.terraria NixOS module.

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The first commit fixes the ExecStop script of the service.
When launching the server without configuring a world to start automatically, the server will show a world selection prompt. The ExecStop script would unconditionally send the exit command to the tmux session, even if the server was still in the world selection phase (during which the exit command doesn't work).
This PR makes it so that if we're still in the world selection phase (checked using shell pattern matching), we will just send a kill-session command instead, since we've got nothing to save.

Some other small changes include factoring out tmux -S terraria.sock calls and using writeShellScript instead of writeScript.

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The other commit moves the module over to using a config file, instead of passing a bunch of command line flags.
The benefit of this other than readability is that the config file has more settings than what could be configured using the flags.

The few extra options I've implemented were the autoCreatedWorldSeed and autoCreatedWorldDifficulty.
These autoCreated* options should probably be factored out into autocreate.worldType autocreate.seed and autocreate.difficulty, but I haven't done them yet.

I added all supported flags to the list, but didn't implement all of them. I'll do that in another PR.

I also removed the top-level with lib; which is an anti-pattern.

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@ncfavier - the other maintainer of the terraria-server package.
Not sure how else I should ping, since this module is very outdated.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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