Add world validation command to mudtool

- Introduced a new command `validate` to check the integrity of world data, ensuring all referenced entities (NPCs, objects, guilds, races, classes, spells) exist and have valid attributes.
- Updated help message to include usage of the new command and its options.
- Added support for specifying a world directory via command line argument.

.gitea/workflows/smoke-tests.yml

@@ -12,7 +12,9 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Install Rust
-        run: sudo apt install -y cargo
+        run: |
+          sudo apt update
+          sudo apt install -y cargo
 
       - name: Build
         run: cargo build