What does this PR do?

This PR enables support for adding a hook to the test events in CI Visibility.
To enable it, we need to call the hook using a linkname because we don't want to expose it to customers yet (we are going to use internally in some repos).

Motivation

There's an internal case where a subtest should be tagged after a parent test has finished so we need to have a way to get all the tests generated by the library before closing them and send them to the backend.

Note: By setting the hook we are actively delaying all the finish() calls to the underlying span, so memory increases are expected and another reason to not make this available in the public api. If we don't set a hook we keep the same current behaviour, closing the span after the test finishes.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running golangci-lint run locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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