Import all sampled Gecko threads

[chicoxyzzy]

Depends on discoveryjs#15.

What

• Import every sampled Gecko or Samply thread as a CPUpro profile.
• Preserve source order and remap the initially selected thread after empty or incomplete threads are skipped.
• Keep the largest selected or sampled thread as the initial view.

Why

Samply recordings can contain main, worker, and helper threads. Selecting only one thread hides recorded CPU work, while CPUpro already supports multi-profile sets.

Impact

Single-thread profiles keep the same behavior. No input or metadata format changes are introduced.

Checks

• npm test
• npm run typecheck
• npm run lint
• npm run build
• git diff --check