World Play Time Reborn

**What's new?**
- **Fixed play time calculation** — the world indicator now shows **your own** play time (read from your player stats file) instead of the sum of all players who ever played the world, so it matches the in-game Statistics screen ([#2](https://github.com/korovagg/WorldPlayTimeReborn/issues/2)).
- If your account has no stats file in a world, the play time of all players is shown as a fallback, so the indicator doesn't disappear.
- **New option: "Count Play Time Of All Players"** — restores the old world-total behavior if you prefer it.
- **New: world save size** — the save-directory size is now displayed beneath the play time in the world selection screen, with a new **"Show World Size"** option (enabled by default) (feature from PR #1 by [@deanxbox](https://github.com/deanxbox)).
- Fixed the missing mod icon in the 1.21.11 and 26.1.2 NeoForge builds.