[DOC] Add DLinear v2 tutorial notebook

[chetana1410]

Reference Issues/PRs

Fixes #2390.

What does this implement/fix? Explain your changes.

Adds a v2 tutorial notebook for DLinear and registers it in docs/source/tutorials_v2.rst.

The notebook builds a small numeric dataset, then walks through:

• TimeSeries
• TslibDataModule (context window, forecast horizon, scalers, metadata)
• DLinear_pkg_v2.fit and DLinear_pkg_v2.predict

DLinear's current v2 implementation uses continuous features only, so the toy series has no categorical columns. The split is by series, with enough series for a non-empty train, validation, and test slice.

Ran the notebook locally. Training completed for 5 epochs, and predict returned forecasts of shape (290, 4).

What should a reviewer concentrate their feedback on?

• Whether the notebook matches the intended v2 tutorial style next to the TFT and TimeXer notebooks.
• The trainer settings (accelerator="cpu", no checkpoint, no logger) used so the example stays small.

Did you add any tests for the change?

No. This is a documentation-only change. nbsphinx_execute is never, so the notebook is not executed in the docs build. It was executed locally.

Any other comments?

Pre-commit hooks were run on the changed files (nbqa-black, nbqa-ruff, nbqa-check-ast).

PR checklist

• The PR title starts with either [ENH], [MNT], [DOC], or [BUG]. [BUG] - bugfix, [MNT] - CI, test framework, [ENH] - adding or improving code, [DOC] - writing or improving documentation or docstrings.
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks. Install hooks with pre-commit install.
  To run hooks independent of commit, execute pre-commit run --all-files

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