Support asynchronous custom formula functions Validated

Feature Description

Provide support in the spreadsheet component for asynchronous custom formulas so users can define functions that return results asynchronously (via promises or async/await). This is needed to integrate external data sources and perform time-consuming operations (e.g., API calls) from formulas. The feature must prevent formulas from rendering as "[object Promise]" and ensure cells display resolved values when the asynchronous operation completes. It must also allow asynchronous functions to be used inside other custom-defined functions without breaking evaluation or rendering.

Requirements

• Mandatory functionality:
• Support custom formula functions that return a Promise or are declared async, and ensure the spreadsheet evaluates and renders the resolved value once the promise settles.
• Ensure using an async call inside a custom-defined function (including nested custom functions) does not result in the cell showing [object Promise].
• Ensure await can be used inside custom functions (i.e., the function can be async) and the engine handles the returned promise by updating the cell when resolved.
• Behavioral expectations:
• When a custom function returns a promise, the cell should show a pending state if applicable, then update to the resolved value.
• Errors or rejected promises should be surfaced meaningfully (e.g., the cell displays an error message/state).
• API expectations:
• Accept user-defined custom functions that return either synchronous values or promises (no change to how users define functions aside from using async/promise semantics).
• Data/formatting rules:
• Resolved values should be rendered according to existing cell formatting rules.