Add NTCIR Tip-of-the-Tongue

**Dataset Information:*

This adds the datasets for the NTCIR 2026 Tip-of-the-Tongue shared task.

**Links to Resources:**

The shared task is described here: https://ntcir-tot.github.io/
The dataset is hosted on Zenodo: https://zenodo.org/records/18777084

**Dataset ID(s) & supported entities:**

- ntcir-tot/2026/

**Checklist**

Mark each task once completed. All should be checked prior to merging a new dataset.

- [ ] Dataset definition (in `ir_datasets/datasets/[topid].py`)
- [ ] Tests (in `tests/integration/[topid].py`)
- [ ] Metadata generated (using `ir_datasets generate_metadata` command, should appear in `ir_datasets/etc/metadata.json`)
- [ ] Documentation (in `ir_datasets/etc/[topid].yaml`)
- [ ] Documentation generated in https://github.com/seanmacavaney/ir-datasets.com/
- [ ] Downloadable content (in `ir_datasets/etc/downloads.json`)
- [ ] Download verification action (in `.github/workflows/verify_downloads.yml`). Only one needed per `topid`.
- [ ] Any small public files from NIST (or other potentially troublesome files) mirrored in https://github.com/seanmacavaney/irds-mirror/. Mirrored status properly reflected in `downloads.json`.