feat: add count function

It introduces a new `count` function that take:
- the grid arena
- X and Y as `isize`

It counts how many nearby cells are alive at a specified position and returns the total.

src/main.rs

@@ -15,9 +15,36 @@ fn display(grid: &[[bool; WIDTH]; HEIGHT], buffer: &mut String) {
     println!("{}", buffer);
 }
 
+fn count(grid: &[[bool; WIDTH]; HEIGHT], x: usize, y: usize) -> u8 { 
+    let near:[(isize, isize); 8] = [
+        (-1, -1), (-1, 0), (-1, 1),
+         (0, -1),           (0, 1),
+        ( 1, -1),  (1, 0),  (1, 1)
+    ];
+
+    let mut count = 0;
+
+    for (i, j) in near {
+        let nx: isize = x as isize + i;
+        let ny: isize = y as isize + j;
+
+        if (nx > 0 && (WIDTH as isize) > nx && 
+            ny > 0 && (HEIGHT as isize) > ny) {
+            
+            if (grid[nx as usize][nx as usize]) {
+                count += 1;
+            }
+        }
+    }
+
+    return count;
+}
+
 fn main() {
     let grid: [[bool; WIDTH]; HEIGHT] = [[false; WIDTH]; HEIGHT];
     let mut buffer: String = String::new();
     
-    display(&grid, &mut buffer);
+    loop {
+        display(&grid, &mut buffer);
+    }
 }