feat: physics2d Cardinal integration tests

[AnthonyWadham]

TL;DR

Removes detailed comment from physics collider field and adds comprehensive Cardinal-driven integration tests for the physics2d plugin.

What changed?

• Removed detailed comment from GroupIndex field in ColliderShape struct, keeping only the field declaration
• Created extensive Cardinal-driven integration tests (cardinal_integration_test.go) for the physics2d plugin that:
  • Tests a complete physics scene with floor, ball, sensor, walls, triangle, and compound bodies
  • Verifies contact/trigger events, query APIs (raycast, AABB overlap, circle sweep), and incremental reconciliation
  • Simulates crash scenarios with ResetRuntime() to test synthetic event generation
  • Validates entity creation, destruction, and transform updates during simulation
  • Uses reflection to access Cardinal's internal ECS world initialization for manual world driving

How to test?

Run the new integration test:

go test ./pkg/plugin/physics2d/test/

The test creates a Cardinal world, registers the physics plugin, runs 360+ ticks of simulation, and validates physics behavior including collision detection, query operations, and crash recovery scenarios.

Why make this change?

The comprehensive integration tests provide end-to-end validation of the physics2d plugin's integration with Cardinal, ensuring proper system event handling, query functionality, and crash recovery behavior that unit tests cannot cover. The tests verify the complete tick lifecycle (PreUpdate reconcile, Update step, PostUpdate) and validate that the plugin correctly handles ECS changes, entity lifecycle events, and runtime crashes with proper recovery.

[AnthonyWadham]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: physics2d Cardinal integration tests #881 👈 (View in Graphite)
• refactor: merge Rigidbody2D and Collider2D into PhysicsBody2D #886
• feat: add ShapeTypeStaticChainLoop and ShapeTypeEdge collider shapes #883
• feat: add Box2D physics2d plugin with CGO #880 : 1 other dependent PR (#882 )
• main

---

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[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
193	2	191	4

View the top 2 failed test(s) by shortest run time

::TestMain

Stack Traces | 0s run time

to reproduce: TEST_SEED=0x69d6aeb2
panic: test timed out after 10m0s
	running tests:
		TestArchetype_ModelFuzz (10m0s)

goroutine 574757 [running]:
testing.(*M).startAlarm.func1()
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:2682 +0x345
created by time.goFunc
	.../hostedtoolcache/go/1.25.5.../src/time/sleep.go:215 +0x2d

goroutine 1 [chan receive, 9 minutes]:
testing.tRunner.func1()
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:1891 +0x451
testing.tRunner(0xc000182fc0, 0xc000235c70)
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:1940 +0x123
testing.runTests(0xc0001aa288, {0xedf940, 0x18, 0x18}, {0x7?, 0xc0001ad3c0?, 0xee8fe0?})
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:2475 +0x4b4
testing.(*M).Run(0xc0001a1040)
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:2337 +0x63a
main.main()
	_testmain.go:101 +0x9b

goroutine 21 [runnable]:
math/rand/v2.(*Rand).uint64n(0xc0001a7300, 0x1)
	.../hostedtoolcache/go/1.25.5.../rand/v2/rand.go:81 +0xc5
math/rand/v2.(*Rand).IntN(...)
	.../hostedtoolcache/go/1.25.5.../rand/v2/rand.go:195
github..../cardinal/internal/ecs.TestArchetype_ModelFuzz(0xc000183180)
	.../internal/ecs/archetype_internal_test.go:86 +0x14b5
testing.tRunner(0xc000183180, 0xa4ed98)
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:1934 +0xea
created by testing.(*T).Run in goroutine 1
	.../hostedtoolcache/go/1.25.5.../src/testing/testing.go:1997 +0x465
FAIL	github..../cardinal/internal/ecs	600.020s

github.com/argus-labs/world-engine/pkg/cardinal/internal/ecs::TestArchetype_ModelFuzz

Stack Traces | 0s run time

=== RUN   TestArchetype_ModelFuzz
=== PAUSE TestArchetype_ModelFuzz
=== CONT  TestArchetype_ModelFuzz

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