fix(ui): speed up detector threshold slider keypresses in test (#123078)

## Why

`projectPerformance` Consecutive DB detector threshold case was hitting
the default **5s** jest timeout on frontend deploys.

## Root cause

Not an ancient flake — regression from the scraps migration
([#119187](https://github.com/getsentry/sentry/pull/119187),
2026-08-10).

**Before scraps**, the test used hold-key syntax in one call:
```ts
await userEvent.keyboard(`{ArrowRight>${indexDelta}}`);
```

**After scraps**, it became a per-key await loop (hold syntax
under-steps the React Aria/scraps slider by 1). The Consecutive DB case
does **17** steps (`100 → 5000`). Under deploy/CI load that blows the 5s
default timeout. Solo it still usually passes.

## Fix

Keep per-key presses (correct for scraps slider), but use
`userEvent.setup({delay: null})` so large deltas stay under 5s.

## Verify

`pnpm test-ci
static/app/views/settings/projectPerformance/projectPerformance.spec.tsx`
→ **50/50**.

<!-- junior-request-attribution:start -->
Requested by **telkins**.
<!-- junior-request-attribution:end -->

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Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Trevor Elkins <trevor.elkins@sentry.io>