Server class code cleanups (#9769)

* Server::overrideDayNightRatio doesn't require to return bool
There is no sense to sending null player, the caller should send a valid object

* Server::init: make private & cleanup
This function is always called before start() and loads some variables which can be loaded in constructor directly.
Make it private and call it directly in start

* Split Server inventory responsibility to a dedicated object

This splits permit to found various historical issues:
* duplicate lookups on player connection
* sending inventory to non related player when a player connects
* non friendly lookups on detached inventories ownership

This reduce the detached inventory complexity and also increased the
lookup performance in a quite interesting way for servers with thousands
of inventories.

src/main.cpp

@@ -887,7 +887,6 @@ static bool run_dedicated_server(const GameParams &game_params, const Settings &
 			// Create server
 			Server server(game_params.world_path, game_params.game_spec,
 					false, bind_addr, true, &iface);
-			server.init();
 
 			g_term_console.setup(&iface, &kill, admin_nick);
 
@@ -922,7 +921,6 @@ static bool run_dedicated_server(const GameParams &game_params, const Settings &
 			// Create server
 			Server server(game_params.world_path, game_params.game_spec, false,
 				bind_addr, true);
-			server.init();
 			server.start();
 
 			// Run server