refactor(workflow): convert all plugins to class/struct + factory pattern

- Python: class extending NodeExecutor + factory.py (80+ plugins)
- TypeScript: class implements NodeExecutor + factory.ts (7 groups, 116 classes)
- Go: struct with methods + factory.go (36 plugins)
- Rust: struct impl NodeExecutor trait + factory.rs (54 plugins)
- Mojo: struct + factory.mojo (11 plugins)

All package.json files now include:
- files array listing source files
- metadata.class/struct field
- metadata.entrypoint field

This enables a unified plugin loading system across all languages
with no import side effects (Spring-style DI pattern).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

workflow/plugins/python/string/string_split/string_split.py

@@ -1,15 +1,19 @@
 """Workflow plugin: split string."""
 
+from ...base import NodeExecutor
 
-def run(_runtime, inputs):
+
+class StringSplit(NodeExecutor):
     """Split string by separator."""
-    text = inputs.get("text", "")
-    separator = inputs.get("separator", " ")
-    max_splits = inputs.get("max_splits")
 
-    if max_splits is not None:
-        result = text.split(separator, max_splits)
-    else:
-        result = text.split(separator)
+    node_type = "string.split"
+    category = "string"
+    description = "Split string by separator"
 
-    return {"result": result}
+    def execute(self, inputs, runtime=None):
+        text = str(inputs.get("text", inputs.get("value", "")))
+        separator = inputs.get("separator", " ")
+        max_splits = inputs.get("max_splits", inputs.get("limit"))
+        if max_splits is not None:
+            return {"result": text.split(separator, max_splits)}
+        return {"result": text.split(separator)}