docs: update contributing, pull request template and license year

[vplasencia]

Description

This PR updates the contributing file, pull request template and license year.

Related Issue(s)

Re zk-kit/zk-kit#396

Checklist

• I have read and understand the contributor guidelines and code of conduct.
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have run yarn style without getting any errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Important

We do not accept minor grammatical fixes (e.g., correcting typos, rewording sentences) unless they significantly improve clarity in technical documentation. These contributions, while appreciated, are not a priority for merging. If there is a grammatical mistake, please feel free to message the team.