Setup tests

- Install Gut using gd-plug.
- Add some basic tests.
- Update workflow to run tests.
- Add test and gd-plug install/uninstall recipes to Justfile.
- Re-enable debug builds as these are used by editor when testing.

test/test_terminal.gd

@@ -0,0 +1,38 @@
+class_name TerminalTest extends GutTest
+
+var terminal: Terminal
+
+
+func before_each():
+	terminal = Terminal.new()
+	terminal.size = Vector2(400, 200)
+	add_child_autofree(terminal)
+
+
+class TestBell:
+	extends TerminalTest
+
+	func test_bell() -> void:
+		watch_signals(terminal)
+		terminal.bell_cooldown = 0
+		terminal.write(char(7))
+		terminal.write(char(0x07))
+		terminal.write("\a")
+		terminal.write("\u0007")
+		terminal.write("'Ask not for whom the \a tolls; it tolls for thee' - John Donne")
+		assert_signal_emit_count(terminal, "bell", 5)
+
+
+class TestCursorPos:
+	extends TerminalTest
+
+	func test_get_cursor_pos_initial():
+		assert_eq(terminal.get_cursor_pos(), Vector2.ZERO)
+
+	func test_get_cursor_pos_x():
+		terminal.write("_")
+		assert_eq(terminal.get_cursor_pos().x, 1)
+
+	func test_get_cursor_pos_y():
+		terminal.write("_".repeat(terminal.cols + 1))
+		assert_eq(terminal.get_cursor_pos().y, 1)