feat: Move end span after children finish

[astuyve]

What does this PR do?

In theory the tracer will flush when all spans finish. I moved this just before merging this feature, but now think it best to move it back to my original location - after child nodes have been traced.

Motivation

Just in case, this should prevent us from attempting to flush after every module load span is created.

Testing Guidelines

Units and integration tests passing should suffice here.

Additional Notes

No

Types of Changes

• [ ] Bug fix
• [ ] New feature
• [ ] Breaking change
• [x] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [ ] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog
• [ ] This PR passes the integration tests (ask a Datadog member to run the tests)