refactor: address code review feedback on heritage extractor

- Simplify makeNode test helper parameter type
- Use !== null check in parse worker for extractFromCall result

Agent-Logs-Url: https://github.com/abhigyanpatwari/GitNexus/sessions/b55df80d-758a-48cd-96de-a7657bdc2acb

Co-authored-by: magyargergo <11230420+magyargergo@users.noreply.github.com>

gitnexus/src/core/ingestion/workers/parse-worker.ts

@@ -1706,7 +1706,7 @@ const processFileGroup = (
                 captureMap['call']!,
                 { filePath: file.path, language },
               );
-              if (heritageItems && heritageItems.length > 0) {
+              if (heritageItems !== null) {
                 for (const item of heritageItems) {
                   result.heritage.push({
                     filePath: file.path,

gitnexus/test/unit/heritage-extraction.test.ts

@@ -40,7 +40,7 @@ interface MockNode {
 }
 
 /** Create a minimal mock SyntaxNode for capture map entries. */
-function makeNode(text: string, type = 'identifier', parent?: MockNode | null): MockNode {
+function makeNode(text: string, type = 'identifier', parent?: MockNode): MockNode {
   return { type, text, parent: parent ?? null };
 }