Fixes for some crashes + behavior enhancements

[otavepto]

• Fix a crash in many Source engine based games due to invalid usage of union in steam_gamestats
• Fix a crash due to invalid usage of union in steam_remote_storage
• Fix invalid overlapping of data in steam_remote_storage due to invalid usage of union
• Fix an incorrect print modifier when parsing mods, resulting in a crash in debug builds
• Fix a potential problem in Steam_User::GetUserDataFolder() where an incomplete path might be copied
• Fix an inverted condition when parsing the ini option matchmaking_server_list_actual_type in configs.main.ini
• Properly handle a scenario where call results might not be triggered in steam_http if the function arg was null
• Create a separate instance of game_stats for servers, client and server instances are requested by games, turns out this is a client/server shared interface
• Add missing callbacks to:
  • steam_remote_storage
  • steam_ugc
  • steam_utils
  • steam_user
  • steam_friends
• Remove duplicate callback triggered in Steam_Friends::SetPersonaName()
• Add potentially missing callback to steam_networking_socketserialized
• ColdClientLoader for Windows:
  • Fix usage of RegQueryValueExW() and RegSetValueExW() (sizeof vs countof), these functions take the buffer size in bytes, not the count of elements:
    https://learn.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regsetvalueexw
    https://learn.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regqueryvalueexw
  • Properly cleanup changed reg keys
  • Fix usage of persistent mode=2
  • Change steam install path and steam exe path in HKCU to point at the loader, and clean them up on exit
  • Change the reg key SourceModInstallPath to point at the folder of the loader, this impacts Source engine based games, cleaned up on exit
  • Avoid adding a backslash at the end of steam install path
• Delete ended game_stats sessions after 15 seconds to reduce memory usage
• Add a new timeline state when the game calls Steam_Timeline::SetTimelineGameMode() to mimic real behavior
• Add comments with default values in the ini files