Rename buildings module to structures

src/app/states/skirmish_states/structures/stone.rs

@@ -0,0 +1,20 @@
+use ratatui::style::Color;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Stone {
+    durability: u16,
+}
+
+impl Stone {
+    pub fn new() -> Self {
+        Self { durability: 1000 }
+    }
+
+    pub fn get_tag(&self) -> char {
+        ' '
+    }
+
+    pub fn get_color(&self) -> Color {
+        Color::White
+    }
+}