feat(sprint-14): add Balloon pop/respawn state machine

test/unit/test_balloon.gd

@@ -0,0 +1,29 @@
+## Tests for Balloon — state machine transitions.
+extends GutTest
+
+var _balloon: Balloon
+
+
+func before_each() -> void:
+	_balloon = Balloon.new()
+	add_child_autofree(_balloon)
+
+
+func test_initial_state_is_idle() -> void:
+	assert_eq(_balloon._state, Balloon.State.IDLE)
+
+
+func test_start_pop_transitions_to_popping() -> void:
+	_balloon._start_pop()
+	assert_eq(_balloon._state, Balloon.State.POPPING)
+
+
+func test_on_pop_complete_transitions_to_popped() -> void:
+	_balloon._on_pop_complete()
+	assert_eq(_balloon._state, Balloon.State.POPPED)
+
+
+func test_on_respawn_complete_transitions_to_idle() -> void:
+	_balloon._state = Balloon.State.RESPAWNING
+	_balloon._on_respawn_complete()
+	assert_eq(_balloon._state, Balloon.State.IDLE)