chore: implement initial bot with substitute command

This commit introduces a Bot struct which is the main type of this
project. The Bot holds a backlog of messages to be able to update a
typo in a message and so on.

So far there is no IRC/TLS implementation, it is only the base logic.

flake.nix

@@ -3,15 +3,17 @@
 
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+    zls.url = "github:zigtools/zls?ref=0.15.0"; # TODO(jsb): Update this when bumping zig version
   };
 
-  outputs = { self, nixpkgs }:
+  outputs = { self, nixpkgs, zls }:
     let
       pkgs = nixpkgs.legacyPackages.x86_64-linux;
     in {
       devShells.x86_64-linux.default = pkgs.mkShell {
         buildInputs = [
           pkgs.zig
+          zls.packages.x86_64-linux.zls
         ];
       };
   };