Sync tutorial notebooks with Colab and link example code in docs

[jhnwu3]

Stacked on #1257. Merge #1257 first; GitHub then retargets this PR to master.

Summary

The repo copies of the tutorial notebooks had drifted from the Colab versions linked in docs/tutorials.rst. The docs also referred to example files by bare names, several of which were wrong.

Changes

• tutorial_pyhealth_medcode.ipynb: now matches the Colab version (Drive 1Tw1AUS53fotH1EYr4Abp7qYN3zDBeUbC), with outputs stripped. Its CrossMap.load("ICD9CM", "ICD10CM") cell needs the icd-mappings backend from medcode: ICD-9 <-> ICD-10 translation and grouper vocabularies via icd-mappings #1257; on master it fails with HTTP Error 404.
• tutorial_pyhealth_data.ipynb, tutorial_pyhealth_trainer.ipynb: synced with Colab. The repo copies still called dataset.patients; BaseDataset now exposes unique_patient_ids.
• docs/tutorials.rst:
  • Each Colab tutorial gets a [Source] link to its notebook in examples/tutorials/.
  • All 74 example filenames now link to the real files. Previously, wrong or renamed paths included EEG_events_SparcNet.py → eeg/eeg_models/SparcNet_eeg_events_classification.py, drug_recommendation_eICU_transformer.py → …_eicu_…, and sleep_staging_* → eeg/sleep_staging/.
  • The readmission list-table is fixed; it wasn't rendering because of a one-space indent.
  • blob/main → blob/master.
  • The file now parses with no docutils warnings (it had 11 before).

Earlier revisions of this PR also changed CrossMap and rewrote the medcode ICD-9 → ICD-10 cell. Those changes are dropped: the clearer missing-table error now lives in #1257, and the Colab cell is correct once #1257 lands.

Testing

• I executed every code cell of the medcode, data and trainer notebooks against this branch, skipping !pip; all pass.
• A script confirmed that every blob/master/examples/… link in tutorials.rst resolves to a file that exists.

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