Bug fixes

1. Fix bug of Sepals living target cache not working when enabled in configs.
2. Fix bug of entity follow range still using 1.21.3 (fixed a value) instead 1.21.4 feature (setting by entity attribute).

Other changes

1. Use HashMap instead of RBTreeMap to improve entities fetch speed.
2. Try to optimize item merge performance, use config key 'enableSepalsItemMerge' to toggle this feature.