[OpenSTEF 4.0] Datasets tutorial notebook

[egordm]

As a user of OpenSTEF 4.0
I want to understand how TimeSeriesDataset and VersionedTimeSeriesDataset work
So that I can correctly use versioned data in forecasting pipelines without data leakage

❗Priority (What if we don't do this?/Are there any deadlines? etc.)

Users cannot learn the core data abstractions without reading source code. The dataset classes are central to the v4.0 API.

Definition of Done:

✅ Acceptance criteria

• Tutorial notebook covers versioned and non-versioned datasets
• Demonstrates all three filter methods with clear visualizations
• Shows select_version and to_horizons workflows
• Executes in Sphinx build without errors
• poe all passes

📄 Documentation criteria:

• Added to docs/source/examples.rst toctree
• Cross-references to API docs resolve correctly

🧪 Test criteria:

• Notebook executes end-to-end (jupytext + Sphinx)
• poe all passes (lint, format, sync)

⌛ Dependencies:

PR #899

🚀 Releasing:

Part of v4.0.0 documentation release

Other information:

🌍 Background

Implementation: PR #899
Parent: #883