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/basic-recon-flow.yaml

@@ -38,7 +38,7 @@ modules:
   - name: port-scan
     depends_on:
       - subdomain-enum
-    condition: "fileLength('{{all_subdomains}}') > 0"
+    condition: "file_length('{{all_subdomains}}') > 0"
     steps:
       - name: setup-ports
         type: bash
@@ -68,7 +68,7 @@ modules:
   - name: screenshot
     depends_on:
       - port-scan
-    condition: "fileLength('{{all_ports}}') > 0"
+    condition: "file_length('{{all_ports}}') > 0"
     steps:
       - name: setup-screenshots
         type: bash