Fix outdated Tutorial_DiscordMERLIN.ipynb

[ShreyasK06]

This PR fixes docs/WIP/Tutorial_DiscordMERLIN.ipynb, which was broken in several ways due to API changes and dependency updates since it was originally written. All changes are scoped strictly to the notebook file.

Fix 1 — core.preprocess now returns 4 values
Updated every T, M_T, Σ_T = core.preprocess(...) call to the correct 4-value unpack (T, M_T, Σ_T, T_subseq_isconstant = core.preprocess(...)), and threaded T_subseq_isconstant through _find_candidates, _get_approx_P, and _refine_candidates so it is passed correctly to core._mass and _prescrump.

Fix 2 — Dead dataset URLs replaced

• NoisySine dataset: original source is gone and no working URL exists. Replaced with a self-contained synthetic signal (sinusoid + noise + spike anomaly) generated with NumPy. No new dependencies required.
• NYC taxi dataset: replaced broken local path with the Zenodo URL provided by the maintainer (https://zenodo.org/record/4276428/files/STUMPY_Basics_Taxi.csv?download=1).

Fix 3 — core._sliding_dot_product renamed
Updated both call sites in _find_candidates and _refine_candidates from core._sliding_dot_product to core.sliding_dot_product.

Fix 4 — np.NINF removed in NumPy 2.0
Replaced all 8 runtime occurrences of np.NINF across _refine_candidates, the MP verification block, _discords, and stumpy_top_k_discords with -np.inf. Occurrences in docstrings and comments were left untouched. No logic changes.

Known issue — pending review discussion
The notebook still fails at out = _discords(T, m, k=15) with:
ValueError: could not broadcast input array from shape (1489,1489) into shape (1489,)
This is caused by stumpy.scrump._prescrump now returning a 2D (l, k) array instead of the 1D (l,) shape _get_approx_P expects. Fix is pending maintainer input.

Closes #1127

[gitnotebooks]

Found 1 changed notebook. Review the changes at https://app.gitnotebooks.com/stumpy-dev/stumpy/pull/1156

[github-actions]

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