Dynamic Unit for Number and Math columns (bind Unit to another column)

## Summary
Allow the Number/Math column’s Unit input to be dynamic by binding it to another column (including computed columns), so each row displays the correct unit automatically.

## Current Problem
The Unit is a static manual entry. When units vary per row or depend on logic (currency, measurement system, category), builders must type and maintain it manually, or ignore it and create multiple templates and ITE for the final display, causing extra work to create these columns and reducing clarity when working in the GDE.

## Desired Outcome
Enable the Unit input in Number/Math column settings to accept a column binding. The Unit shown for a value updates per row as the bound column changes.

## Examples / Scenarios
- Currency: Price Number column’s Unit reads from display_currency (USD/EUR) computed column.
- Locale: Distance Number column’s Unit uses unit_pref (km/mi) derived from the user’s profile.
- Category: Inventory quantity’s Unit comes from a Category->Lookup (“kg”, “L”, “pcs”).

## Why This Matters
Avoid extra work just for UI, reduces manual maintenance and errors, improves clarity for builders in the GDE, keeps numeric formatting/validation benefits

## Alternatives Today
Creating templates per unit + ITE for final display, conditional components