Move server calls to MusicServerClient and give players stable ids

Server requests move out of Settings into a new MusicServerClient
autoload with one function per endpoint. It sends requests through a
swappable HttpTransport so tests can fake the server, and it frees its
HTTPRequest nodes after use.

Players now have a UUID that never changes. Their position in
Settings.player_array is only used for the Alt+<number> keybinds.
Previously the position doubled as the id, so removing a player made
points and wins land on the wrong player, and could delete another
player's point from a song.

Also fixes:
- format_time showed 59.6 seconds as "00:60"
- searches containing regex characters such as "Q*bert" broke search
- SongObject and PlayerObject were Nodes that were never freed; they
  are now RefCounted
- search matching is split out of the UI code into find_matches()

Player.gd

@@ -19,15 +19,19 @@ var remove_player := $HBoxContainer/RemovePlayer
 signal change_character_clicked
 signal player_removed
 
-@export
-var id: int
+## The player shown in this row.
+var player_object: PlayerObject
+
+## Position in Settings.player_array. Only used for the keybinds: Alt+<list_index + 1>
+## gives this player a point and Ctrl+Alt+<list_index + 1> takes one away.
+var list_index: int
 
 # Called when the node enters the scene tree for the first time.
 func _ready() -> void:
 	add_button.pressed.connect(add_point)
-	add_button.set_shortcut(create_button_shortcut(id, false))
+	add_button.set_shortcut(create_button_shortcut(list_index, false))
 	minus_button.pressed.connect(minus_point)
-	minus_button.set_shortcut(create_button_shortcut(id, true))
+	minus_button.set_shortcut(create_button_shortcut(list_index, true))
 	character.pressed.connect(change_character)
 	remove_player.pressed.connect(func() -> void: player_removed.emit())
 	update_score()
@@ -36,21 +40,21 @@ func _ready() -> void:
 func _process(delta: float) -> void:
 	remove_player.visible = Settings.edit_players
 
-func create_button_shortcut(scancode : int, ctrl_pressed: bool) -> Shortcut:
+func create_button_shortcut(index: int, ctrl_pressed: bool) -> Shortcut:
 	var button_shortcut: Shortcut = Shortcut.new()
 	var button_event : InputEventKey = InputEventKey.new()
-	button_event.keycode = scancode + 49
+	button_event.keycode = KEY_1 + index
 	button_event.alt_pressed = true
 	button_event.ctrl_pressed = ctrl_pressed
 	button_shortcut.events.append(button_event)
 	return button_shortcut
 
 func add_point() -> void:
-	Settings.player_array[id].add_point()
+	player_object.add_point()
 	update_score()
 
 func minus_point() -> void:
-	Settings.player_array[id].minus_point()
+	player_object.minus_point()
 	update_score()
  
 func change_character() -> void:
@@ -58,22 +62,22 @@ func change_character() -> void:
 
 func character_selected(file_name: String) -> void:
 	print("Back in player list with: " + file_name)
-	Settings.player_array[id].character = load("res://characters/" + file_name)
+	player_object.character = load("res://characters/" + file_name)
 	set_player_character()
 	
 func new_character_selected(character_texture: ImageTexture) -> void:
 	print("Back in player list with new")
-	Settings.player_array[id].character = character_texture
+	player_object.character = character_texture
 	set_player_character()
 
 func set_player_character() -> void:
 	character.custom_minimum_size = Vector2(80, 40)
 	character.ignore_texture_size = true
 	character.stretch_mode = TextureButton.STRETCH_KEEP_ASPECT_CENTERED
-	character.texture_normal = Settings.player_array[id].character
+	character.texture_normal = player_object.character
 
 func update_score() -> void:
 	if OS.has_feature("debug"):
-		player_name_field.text = str(Settings.player_array[id].id) + " " + Settings.player_array[id].player_name + ": " + str(Settings.player_array[id].player_score)
+		player_name_field.text = str(list_index + 1) + " " + player_object.player_name + ": " + str(player_object.player_score)
 	else:
-		player_name_field.text = Settings.player_array[id].player_name + ": " + str(Settings.player_array[id].player_score)
+		player_name_field.text = player_object.player_name + ": " + str(player_object.player_score)