feat: add rain puddles and stabilize shoreline water

tests/rain_puddle_runtime_validation.gd

@@ -0,0 +1,84 @@
+extends SceneTree
+
+const MainScene: PackedScene = preload("res://main/main.tscn")
+
+
+func _initialize() -> void:
+	call_deferred("_run")
+
+
+func _run() -> void:
+	root.size = Vector2i(1280, 720)
+	var main: Node = MainScene.instantiate()
+	root.add_child(main)
+	for _frame: int in 4:
+		await process_frame
+	if not bool(main.get("_application_initialized")):
+		main.call("_activate_selected_data_path", "", true)
+	for _frame: int in 8:
+		await process_frame
+	assert(bool(main.get("_application_initialized")))
+	assert(bool(main.call(
+		"_apply_world",
+		WorldLayout.GENERATED,
+		PlayerSaveManager.DEFAULT_WORLD_SEED,
+		true,
+	)))
+	var weather := main.get_node(
+		"%WorldWeatherService"
+	) as WorldWeatherService
+	assert(weather != null)
+	weather.apply_authoritative_snapshot(
+		WorldWeatherService.Weather.RAINY,
+		60.0,
+	)
+	main.call("_set_gameplay_active", true)
+	await physics_frame
+	await physics_frame
+
+	var puddles := main.get_node(
+		"RainPuddlePresentation"
+	) as RainPuddlePresentation
+	assert(puddles != null)
+	assert(not puddles.is_light_performance_profile())
+	assert(puddles.is_processing())
+	puddles.set_suppressed(true)
+	assert(not puddles.is_processing())
+	puddles.set_suppressed(false)
+	assert(puddles.is_processing())
+	puddles.set_active(false)
+	assert(not puddles.is_processing())
+	puddles.set_active(true)
+	assert(puddles.is_processing())
+	for _tick: int in 18:
+		puddles.call("_process", 0.25)
+	assert(puddles.get_active_puddle_count() > 0)
+	var visual_root := puddles.get_node("PuddleVisuals") as Node3D
+	assert(visual_root != null)
+	for puddle_visual: Node in visual_root.get_children():
+		assert(puddle_visual is MeshInstance3D)
+		assert(puddle_visual.get_child_count() == 0)
+
+	weather.apply_authoritative_snapshot(
+		WorldWeatherService.Weather.SUNNY,
+		60.0,
+	)
+	puddles.call("_process", 30.0)
+	assert(puddles.get_active_puddle_count() == 0)
+	_stop_audio_players(main)
+	main.queue_free()
+	for _frame: int in 8:
+		await process_frame
+	print("Rain puddle runtime validation: PASS")
+	quit()
+
+
+func _stop_audio_players(root_node: Node) -> void:
+	if root_node is AudioStreamPlayer:
+		(root_node as AudioStreamPlayer).stop()
+	elif root_node is AudioStreamPlayer2D:
+		(root_node as AudioStreamPlayer2D).stop()
+	elif root_node is AudioStreamPlayer3D:
+		(root_node as AudioStreamPlayer3D).stop()
+	for child: Node in root_node.get_children():
+		_stop_audio_players(child)