[EuiQuickSelect] Migrate from class to function component

[weronikaolejniczak]

EuiQuickSelect provides time unit arithmetic controls (e.g., "Last 15 minutes") within EuiSuperDatePicker's quick select popover.

• File: components/date_picker/super_date_picker/quick_select_popover/quick_select.tsx
• Class size: 249 lines
• State: timeTense, timeValue, timeUnits
• Lifecycle: None

Migration notes:

No lifecycle methods. State is straightforward. Complexity is in the time arithmetic validation logic. Internal to SuperDatePicker.

Acceptance criteria:

• Convert to function component with useState
• Maintain time arithmetic and validation
• All existing tests pass