the localstack container occasionally fails to start

An occasional flaky test issue is that the localstack container (used for AWS SDK tests) fails to start.

A recent example: https://github.com/elastic/apm-agent-nodejs/actions/runs/14646457344/job/41101781884#step:2:672

```
Service container localstack failed.
/usr/bin/docker logs --details ac35d4b8f9c7b300fee2ba0d0baacf06e4bc793be75e857ff661ee279ee5bd12

LocalStack version: 3.0.0
LocalStack build date: 2023-11-16
LocalStack build git hash: 3cd32364

2025-04-24T16:17:07.780 WARN --- [ MainThread] localstack.deprecations : DATA_DIR is deprecated (since 1.0.0) and will be removed in upcoming releases of LocalStack! Please use PERSISTENCE instead. The state will be stored in your LocalStack volume in the state/ directory.
Error: Failed to initialize container localstack/localstack:3.0.0
Error: One or more containers failed to start.
```

(I don't think the `DATA_DIR is deprecated` warning is relevant, though I suppose it might be.)

I think we should consider dropping localstack and using small (nock-based, perhaps) mock tests for aws-sdk testing.