Update copyright year to 2026 and consolidate authors

[psinger-prior]

Issue

N/A

Motivation and Context

This PR updates the copyright year from 2025 to 2026 across the codebase and consolidates the authors list in pyproject.toml to a single organizational entry for Prior Labs with a contact email.

Changes Made:

1. pyproject.toml: Replaced the detailed list of individual contributors with a single organizational author entry: [{ name = "Prior Labs", email = "opensource@priorlabs.ai" }]
2. Copyright headers: Updated all copyright year references from 2025 to 2026 in:
   • README.md
   • All example files
   • All source files in src/tabpfn/

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Public API Changes

• No Public API changes

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How Has This Been Tested?

No testing needed. These are metadata and documentation updates with no functional code changes.

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Checklist

• The changes have been tested locally.
• Documentation has been updated (copyright year in README).
• A changelog entry has been added (no changelog needed - administrative update)
• The code follows the project's style guidelines.
• I have considered the impact of these changes on the public API (none).

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[gemini-code-assist]

Code Review

This pull request updates the copyright year from 2025 to 2026 across the entire codebase, including the README, example scripts, and source files. Additionally, it simplifies the author metadata in pyproject.toml by replacing the list of individual contributors with a single entry for Prior Labs. No review comments were provided for this pull request, and I have no feedback to provide.

[CLAassistant]

All committers have signed the CLA.