Update JavaScript test optimization docs

[juan-fernandez]

What does this PR do? What is the motivation?

Updates the JavaScript and TypeScript Test Optimization setup documentation to:

• Split supported framework versions for dd-trace v5 and v6 into tabs, with v6 shown first.
• Document Vitest test.concurrent support versions and the optional DD_EXPERIMENTAL_TEST_OPT_VITEST_NO_WORKER_INIT optimization flag.
• Update Playwright custom tags and measures to use the active test span directly.
• Remove obsolete Cypress pre-10 setup guidance and the Jest --workerThreads known limitation.
• Update DD_TEST_SESSION_NAME default behavior for dd-trace v6.

No Jira ticket.

Merge readiness

• Ready for merge

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AI assistance

Used Codex for documentation edits, GitHub source checks, and local verification.

Additional notes

Validation:

• git diff --check
• git verify-commit HEAD

Vale could not be run locally because vale is not installed on PATH.

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/juan-fernandez/update-js-test-optimization-docs/tests/setup/javascript
• https://docs-staging.datadoghq.com/juan-fernandez/update-js-test-optimization-docs/tests/troubleshooting/

[juan-fernandez]

/review

[github-actions]

🤖 Automated review by Claude. AI-generated; verify before acting.

Content updates look accurate and consistent with the v5/v6 split throughout the page. A few clarity and scannability nits on the new experimental Vitest paragraph (which is duplicated across both files) and the DD_TEST_SESSION_NAME default definition. Nothing blocking.

_{Reviewed 0c124a18d4a449751fe044aaf82c1a9aab6b27e2 — workflow run}