ENH: Update download_all_regression to use extended TSER 2024 archive

[devesh-047]

Description

download_all_regression() currently downloads the original TSER archive
containing 19 datasets, while load_regression() supports 63 regression
datasets listed in tser_soton.

This PR updates the download source to the extended TSER regression archive
published on Zenodo in May 2024, which contains all 63 datasets.

Zenodo record:
https://zenodo.org/records/11236865

Scope of change

• Update download URL only
• No changes to dataset definitions or loading logic

Notes

The extended archive is approximately 900 MB. A short note has been added
to the docstring to make this explicit.

Fixes #3073

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