Start updating tardy to Zig 0.15.1

[bernardassan]

currently just done enough changes to get examples and tests passing

Enable llvm for building exe's to prevent error: undefined symbol: tardy_swap_frame

Pass args to examples in build.zig

[bernardassan]

@mookums, instead of making this PR very big, I will make it small and do consecutive updates for the new Io API after this.

I would appreciate it if you could review this PR at your earliest convenience.

[mookums]

Hi, would prefer if we could have one PR for upgrading to 0.15.1. I can take a look at this one now but would prefer to take one look at the end.

[bernardassan]

Okay then, I will move the Reader & Writer updates to this PR

[bernardassan]

@mookums, this PR is Ready for review

[mookums]

@bernardassan Just saw this, will review tomorrow afternoon 🎆

[bernardassan]

That'd be nice

[mookums]

@bernardassan e2e test seems to work locally (on Linux) so that's a good sign!

1. You should update the CI workflow to use the 0.15.1 zig verison, that way the tests will properly run.
2. You should also update the flake.nix to use the proper dependencies for 0.15.1. Here is a correct one:

{
  description = "an asynchronous runtime for Zig";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/release-25.05";

    zigPkgs.url = "github:mitchellh/zig-overlay";
    zigPkgs.inputs.nixpkgs.follows = "nixpkgs";

    zlsPkg.url = "github:zigtools/zls/0.15.0";
    zlsPkg.inputs.zig-overlay.follows = "zigPkgs";
    zlsPkg.inputs.nixpkgs.follows = "nixpkgs";

    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs =
    {
      nixpkgs,
      zigPkgs,
      zlsPkg,
      flake-utils,
      ...
    }:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        overlays = [
          (final: prev: {
            zigpkgs = zigPkgs.packages.${prev.system};
            zls = zlsPkg.packages.${prev.system}.default;
          })
        ];
        pkgs = import nixpkgs { inherit system overlays; };
      in
      {
        devShells.default = pkgs.mkShell {
          packages = with pkgs; [
            zigpkgs."0.15.1"
            zls
            openssl
            inetutils
            wrk
          ];
        };
      }
    );
}