perf: fastutil Long2ObjectOpenHashMap for PlayerMap, zero-allocation ConcurrentIntHashMap, and Java 9-25 timings support

[GamingOP69]

Summary

Optimizes PlayerMap spatial lookup performance, eliminates lambda allocations on ConcurrentIntHashMap, synchronizes explosion density caching, fixes async pathfinding rejection recovery, and adds Java 9–25 version parsing support in CustomTimingsHandler.

Problem & Root Cause

• PlayerMap used Long2ObjectArrayMap, which performs $O(N)$ linear scans per bucket. On servers with large player counts, this degraded performance. Additionally, calling move() before add() caused NullPointerException on uninitialized buckets.
• ConcurrentIntHashMap created unnecessary lambda instances on hot get/put paths in the entity tracker.
• explosionDensityCache in World.java was accessed without synchronization by async TNT calculations.
• In SearchHandler.java, if the async pathfinding executor rejected a task (e.g. queue full), isSearching was never reset, permanently freezing mob navigation.
• CustomTimingsHandler parsed Java versions assuming a single-digit major version format (1.8), which broke on modern Java runtimes (Java 9, 11, 17, 21, 25).

Solution

• Upgraded PlayerMap to Long2ObjectOpenHashMap for $O(1)$ lookups and added bucket presence checks in move().
• Replaced lambda allocations in ConcurrentIntHashMap with direct synchronized methods.
• Added synchronization to explosionDensityCache operations.
• Wrapped async pathfinding task submission with proper isSearching cleanup on rejection.
• Updated CustomTimingsHandler to parse modern JRE version strings (11.0.x, 17.0.x, 21.0.x, 25.x).
• Added unit tests: PlayerMapRegressionTest, IndexedLinkedHashSetRegressionTest, ConcurrentIntHashMapRegressionTest, ExplosionDensityCacheConcurrencyTest, JavaVersionParsingTest, and JavaVersionParsingRegressionTest.

[GamingOP69]

A few performance improvements and a Java compatibility fix.