test: add comprehensive ECS benchmarks

[gauvainw]

What changed and why

Establishes comprehensive benchmarks for all performance-critical ECS paths to enable data-driven optimization via benchstat.

New benchmarks

Benchmark	Description
EntityCreation	NewEntity + 2x Set (position + velocity)
EntityRecycling	Create + Set + Destroy cycle
ArchetypeTransition	Add/Remove component on existing entity
Query1_1k	Query1.Each over 1K entities
Query2_10k	Query2.Each over 10K entities
Query2_100k	Query2.Each over 100K entities
Query3_10k	Query3.Each over 10K entities
Query4_10k	Query4.Each over 10K entities
Query2_Iter_10k	Query2.Iter (Go 1.23 iterator) over 10K
EventBus_SyncDispatch	Synchronous handler dispatch latency
EventBus_AsyncDispatch	Async channel dispatch with background drain
GetComponentValue	Reflection-based component read
SetComponentValue	Reflection-based component write
WorldUpdate_10k	Full Update loop with 10K entities
WorldUpdate_100k	Full Update loop with 100K entities

Baseline results (i5-9300H, linux/amd64)

BenchmarkEntityCreation-8             ~7K ns/op    ~500 B/op    9 allocs/op
BenchmarkEntityRecycling-8            ~3K ns/op     56 B/op     3 allocs/op
BenchmarkArchetypeTransition-8        ~500 ns/op     8 B/op     0 allocs/op
BenchmarkQuery1_1k-8                  ~120 us/op     8 B/op     1 allocs/op
BenchmarkQuery2_10k-8                 ~2 ms/op       8 B/op     1 allocs/op
BenchmarkQuery2_100k-8                ~25 ms/op      8 B/op     1 allocs/op
BenchmarkQuery3_10k-8                 ~3 ms/op       8 B/op     1 allocs/op
BenchmarkQuery4_10k-8                 ~2 ms/op       8 B/op     1 allocs/op
BenchmarkQuery2_Iter_10k-8            ~1 ms/op       8 B/op     1 allocs/op
BenchmarkEventBus_SyncDispatch-8      ~70 ns/op      0 B/op     0 allocs/op
BenchmarkEventBus_AsyncDispatch-8     ~240 ns/op     0 B/op     0 allocs/op
BenchmarkGetComponentValue-8          ~340 ns/op    16 B/op     1 allocs/op
BenchmarkSetComponentValue-8          ~220 ns/op     0 B/op     0 allocs/op
BenchmarkWorldUpdate_10k-8            ~660 us/op     8 B/op     1 allocs/op
BenchmarkWorldUpdate_100k-8           ~13 ms/op      8 B/op     1 allocs/op

How to test

go test -bench=. -benchmem ./internal/ecs/

Related issue

Closes #12

[Copilot]

Pull request overview

Adds a comprehensive benchmark suite for the ECS package to enable consistent performance tracking (e.g., via benchstat) across entity lifecycle, archetype transitions, queries, event dispatch, reflection-based component access, and full-world updates.

Changes:

• Added benchmarks covering entity creation/recycling, archetype transitions, query iteration (including iterator-based), event bus dispatch, reflection component get/set, and world update at multiple scales.
• Introduced a new test-only component type (testDamage) to support Query4 benchmarks.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/ecs/component_test.go	Adds testDamage component type used by new benchmarks.
internal/ecs/benchmark_test.go	Adds a broad ECS benchmark suite for critical performance paths and larger-scale workloads.

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[Copilot]

BenchmarkArchetypeTransition alternates Set/Remove based on the loop index, but the chosen entity also changes each iteration. That means the Remove branch usually targets entities that never had testVelocity, so it mostly exercises the early-return path (no archetype move) rather than a real transition. Consider toggling per-entity state (e.g., track whether each entity currently has testVelocity, or alternate Set/Remove on the same entity) so both add/remove paths actually move between archetypes.

Suggested change

	b.ResetTimer()
	for i := range b.N {
	e := entities[i%len(entities)]
	if i%2 == 0 {
	Set(w, e, testVelocity{DX: 1})
	} else {
	Remove[testVelocity](w, e)
	}
	hasVelocity := make([]bool, len(entities))
	b.ResetTimer()
	for i := range b.N {
	idx := i % len(entities)
	e := entities[idx]
	if hasVelocity[idx] {
	Remove[testVelocity](w, e)
	} else {
	Set(w, e, testVelocity{DX: 1})
	}
	hasVelocity[idx] = !hasVelocity[idx]