feat: add Vitest support

[cbasitodx]

What

Add basic Vitest support to ddtest, including suite-level planning and execution, Vitest-specific dd-trace initialization, native file discovery for Vitest 2 and newer, and config-aware discovery for Vitest 1.6 with a filesystem glob as the final fallback.

Why

ddtest supports JavaScript projects using Jest but cannot currently plan or run Vitest suites. Vitest 1.6 also lacks the list --filesOnly command available in later versions, so it needs a compatibility path that still respects project configuration.

E2E testing

Focused validation completed:

• go test ./internal/framework ./internal/platform

Manual E2E scenario:

1. Configure a JavaScript project with dd-trace-js 5.111 or newer and Vitest 1.6, including custom include/exclude rules or projects.
2. Run ddtest plan --platform javascript --framework vitest and confirm only the files selected by Vitest are planned.
3. Run ddtest run --platform javascript --framework vitest and confirm the selected files execute with Test Optimization instrumentation.
4. Repeat with Vitest 2 or newer to validate native list --filesOnly discovery.

[datadog-datadog-prod-us1]

More details

Vitest 2.1.9 native discovery and the Vitest 1.6 config-aware fallback both returned the expected configured test files, including exclusion and custom-pattern scenarios. Existing Go tests also passed; no clear diff-only behavioral regression was reproduced. No additional tests recommended: the PR already covers the exercised discovery branches and the remaining lint check is blocked by the sandbox toolchain mismatch.

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[chatgpt-codex-connector]

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[datadog-datadog-prod-us1]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 84.62%
• Overall Coverage: 87.41% (-0.16%)

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