test: add benchmark coverage for ExecutorEventHandler performance

[sachin9058]

Summary

This PR adds benchmark coverage for ExecutorEventHandler.HandleEntityEvent to evaluate its performance characteristics.

Currently, there is no benchmark for this critical execution path, making it difficult to understand throughput and memory allocation behavior or detect performance regressions over time. This change introduces both sequential and parallel benchmarks to provide a baseline for future performance analysis.

The benchmarks use a minimal stub executor to isolate handler logic and avoid external dependencies.

No additional dependencies are required for this change.

Fixes #6343

Testing

• Ran benchmarks locally using:
  go test ./internal/engine -bench=.

Benchmark results:

BenchmarkHandleEntityEvent-12 1803787 635.4 ns/op 840 B/op 14 allocs/op
BenchmarkHandleEntityEventParallel-12 2365395 499.8 ns/op 838 B/op 14 allocs/op

• Verified both sequential and parallel benchmarks execute successfully
• Confirmed allocation reporting (allocs/op, B/op)
• Ensured lint checks pass (make lint-fix)

The parallel benchmark shows improved throughput compared to sequential execution, indicating the handler scales well under concurrent workloads.

No functional changes were introduced, as this PR only adds benchmark tests.
No functional changes were introduced, as this PR only adds benchmark tests.

[coveralls]

coverage: 59.327%. remained the same — sachin9058:test/executor-benchmark into mindersec:main