Src, move out of ./rust, add missing wip files

Moves file contents out of ./rust since I'm planning to go with rust for
the backend and the lexicons will be used for codegen soon anyways.

I also added extra files that have been in the works that I have been
accidentally sprinkling into main.rs already. God forbid I need to
cherry-pick anything from so far back in the history.

It will make git blame ugly though.

flake.nix

@@ -0,0 +1,50 @@
+{
+  description = "Example Rust development environment for Zero to Nix";
+
+  # Flake inputs
+  inputs = {
+    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.2405.*.tar.gz";
+    rust-overlay.url = "github:oxalica/rust-overlay"; # A helper for Rust + Nix
+  };
+
+  # Flake outputs
+  outputs = { self, nixpkgs, rust-overlay }:
+    let
+      # Overlays enable you to customize the Nixpkgs attribute set
+      overlays = [
+        # Makes a `rust-bin` attribute available in Nixpkgs
+        (import rust-overlay)
+        # Provides a `rustToolchain` attribute for Nixpkgs that we can use to
+        # create a Rust environment
+        (self: super: {
+          rustToolchain = super.rust-bin.stable.latest.default;
+        })
+      ];
+
+      # Systems supported
+      allSystems = [
+        "x86_64-linux" # 64-bit Intel/AMD Linux
+        "aarch64-linux" # 64-bit ARM Linux
+        "x86_64-darwin" # 64-bit Intel macOS
+        "aarch64-darwin" # 64-bit ARM macOS
+      ];
+
+      # Helper to provide system-specific attributes
+      forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
+        pkgs = import nixpkgs { inherit overlays system; };
+      });
+    in
+    {
+      # Development environment output
+      devShells = forAllSystems ({ pkgs }: {
+        default = pkgs.mkShell {
+          # The Nix packages provided in the environment
+          packages = (with pkgs; [
+            # The package provided by our custom overlay. Includes cargo, Clippy, cargo-fmt,
+            # rustdoc, rustfmt, and other tools.
+            rustToolchain
+          ]) ++ pkgs.lib.optionals pkgs.stdenv.isDarwin (with pkgs; [ libiconv ]);
+        };
+      });
+    };
+}