feat: add LLM step executor with vision and tool support, event workflow system, and inheritance

- Add LLM executor supporting OpenAI vision, tool calling, embeddings, and structured outputs
- Introduce event emitter/receiver workflows with deduplication and filtering (generate_event functions)
- Add workflow extends/override system enabling inheritance chains and step merge modes
- Update function naming to snake_case across all testdata (fileExists→file_exists, etc.)
- Add comprehensive test fixtures for linter, events, CDN, step dependencies, and extends workflows

test/testdata/complex-workflows/vulnerability-flow.yaml

@@ -46,7 +46,7 @@ modules:
   - name: scanning
     depends_on:
       - discovery
-    condition: "fileLength('{{all_endpoints}}') > 0"
+    condition: "file_length('{{all_endpoints}}') > 0"
     steps:
       - name: init-scanning
         type: bash
@@ -95,8 +95,8 @@ modules:
           var findings = [];
           var nucleiFile = "{{nuclei_results}}";
 
-          if (fileExists(nucleiFile)) {
-            var content = readFile(nucleiFile);
+          if (file_exists(nucleiFile)) {
+            var content = read_file(nucleiFile);
             var lines = content.split("\n").filter(function(l) { return l.trim().length > 0; });
             findings = lines.map(function(l) {
               try { return JSON.parse(l); } catch(e) { return {raw: l}; }