perf(server): reuse Entity.tick() event payload to eliminate per-tick allocations

[RZDESIGN]

Summary

Entity.tick() is the server's hottest path — it fires for every entity on every tick (default 20 ticks/s). The current implementation allocates a fresh { entity, tickDeltaMs } object each time and immediately discards it after the event listeners return. With 100+ entities in a world this creates 2 000+ short-lived objects per second, all of which become garbage and pressure the GC into more frequent pauses.

This PR caches the payload as a private field on each Entity instance and only mutates the tickDeltaMs value before emitting. The object reference stays stable across ticks — no allocation, no GC pressure.

Changes

File	Change
server/src/worlds/entities/Entity.ts	Added _tickPayload field, reuse it in tick() instead of allocating a new object

Net diff: +1 field declaration, +1 assignment, −1 object literal (3 meaningful lines).

Risk Assessment

• The event payload type { entity: Entity, tickDeltaMs: number } is unchanged — listeners receive the exact same shape.
• The payload is mutated before emit() and only read during emit() — there is no window where stale data could be observed.
• If a listener were to store a reference to the payload and read it later, they would see the latest tick's tickDeltaMs instead of the one from their tick. This is a theoretical concern only — all existing listeners and the documented pattern consume the value synchronously. If this ever becomes a concern, a Object.freeze() in dev mode could catch it.

Test Plan

• Run a world with 100+ entities and verify EntityEvent.TICK listeners still receive correct tickDeltaMs values
• Monitor server memory / GC pauses before and after — expect measurable reduction in minor GC frequency
• Verify no behavioral change in entity controllers (BaseEntityController.tick still called correctly)