Feature request: Multi-select support for NumericMenu

[web11-ateves]

Feature request

Add optional multi-select behavior to useNumericMenu/<NumericMenu> so users can select multiple numeric ranges (e.g., price).

Motivation

• Ecommerce UIs commonly need multiple price ranges at once (e.g., “$10–$20” OR “$30–$50”).
• Today, NumericMenu is single-select, pushing teams to build custom checkbox UIs and manual <Configure filters> logic.
• First-class multi-select would reduce app complexity, avoid inconsistencies with other widgets, and improve DX.

Current limitation

• State tracks a single value.
• refine replaces the current selection rather than toggling it.

Expected Behavior

• When multiple is set, render checkboxes.
• When multiple is omitted/false, keep the existing single-select radio behavior.
• onChange/refine toggles values in multi-select mode; replaces in single-select mode.

[Haroenv]

What we usually suggest is to precompute the ranges and add them as strings in your records, eg. priceRange: "10 - 20". You can then use a regular refinement list for this UI, which also will have counts available for each of the options, which is hard/impossible for multiple number ranges.