feat: require date_column in training parameters and update documentation

- Made `date_column` a required field in `TrainModelParams`, ensuring it must be present in the input data.
- Updated related documentation in `input-sample.md`, `README.md`, and various test scenarios to reflect the change in requirement.
- Adjusted the handling of `date_format` to default to `yyyy-MM-dd HH:mm:ss` if omitted, enhancing usability.
- Refined test scenarios to include new examples and ensure compliance with the updated parameter structure.

These changes improve the robustness of the model training workflow and clarify the expectations for input data.

e2e/helpers.py

@@ -3,7 +3,9 @@ Shared helpers for E2E tests (Temporal workflows + PostgreSQL).
 """
 
 import asyncio
+import json
 from datetime import datetime
+from pathlib import Path
 from typing import Any
 
 import pytest
@@ -16,7 +18,7 @@ async def start_and_await_workflow(
     workflow_run,
     input_data: dict,
     workflow_id: str,
-    timeout: float = 120.0,
+    timeout: float = 600.0,
 ):
     """
     Start a Temporal workflow and wait for its result.
@@ -26,7 +28,7 @@ async def start_and_await_workflow(
         workflow_run: Workflow run method (e.g. TrainModel.run).
         input_data: Workflow input payload.
         workflow_id: Unique workflow id.
-        timeout: Max seconds to wait for completion.
+        timeout: Max seconds to wait for completion (default allows cold testcontainer startup).
 
     Returns:
         Workflow result value.
@@ -186,9 +188,6 @@ def load_scenario(scenario_filename: str) -> dict[str, Any]:
     Returns:
         dict: Parsed scenario payload.
     """
-    import json
-    from pathlib import Path
-
     scenario_path = (
         Path(__file__).parent.parent / 'docs' / 'test-scenarios' / scenario_filename
     )