fix: support recordError with falsy Error (#253)

## Summary

Support calling `LDObserve.recordError` with falsy value without causing
an error.

## How did you test this change?

CI

## Are there any deployment considerations?

no

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Ensure `recordError` handles nullish values by defaulting to `new
Error('Unknown error')`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
d63bee4. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Vadman97

sdk/highlight-run/src/sdk/observe.ts

@@ -254,6 +254,7 @@ export class ObserveSDK implements Observe {
 		source?: string,
 		type?: ErrorMessageType,
 	) {
+		error = error || new Error('Unknown error')
 		if (error instanceof Error && error.cause) {
 			payload = {
 				...payload,