feat: add display function

This commit introduces a new `display` function:
- It takes an immutable reference to a grid of bool values
- It takes mutable reference to a String buffer.

it writes to the buffer, `X` or `.` depending on the grid's bool element.

Cargo.toml

@@ -1,5 +1,5 @@
 [package]
-name = "GameOfLife_rs"
+name = "GameOfLife"
 version = "0.1.0"
 edition = "2024"