refactor: simplify toPreviewText by removing redundant branches

Array.prototype.join already calls String() on non-nullish elements, so
the .map() was identity after .filter(). The typeof string fast path
returned the same result as the trailing String(text), so it was a no-op
too. Four branches collapse to three with identical behavior.

Side benefit: return String(text) is now the path strings take, fixing
the Codecov uncovered-line flag.

Addresses review feedback:
#14073 (comment)

Author: christian-byrne

src/extensions/core/textPreviewWidgets.ts

@@ -67,13 +67,8 @@ export function addTextPreviewWidgets(node: LGraphNode) {
 }
 
 function toPreviewText(text: unknown): string {
-  if (typeof text === 'string') return text
   if (text == null) return ''
-  if (Array.isArray(text))
-    return text
-      .filter((part) => part != null)
-      .map((part) => (typeof part === 'string' ? part : String(part)))
-      .join('\n\n')
+  if (Array.isArray(text)) return text.filter((part) => part != null).join('\n\n')
   return String(text)
 }