Version bump: 3.0 (#3334)

* version bump 3.0

* update uv.lock (deeplabcut version 3.0)

* Add 3.0 changelog (#3340)

* Add 3.0 changelog

### Contents

- Finalized 3.0 changelog
- Adds benchmark images

### TODO

- [ ] Fix image links to point to github user content on main

* Use raw GitHub URLs for changelog images

Replace relative image paths with raw.githubusercontent.com absolute URLs in changelog/3_0_0/v3_0_0.md so images render correctly when viewed in releases. Updated three image references (openfield_benchmark_pr2613.png, speed_tensorflow.avif, buctd_benchmarks.png).

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Co-authored-by: Cyril Achard <cyril.achard@epfl.ch>
Co-authored-by: Mackenzie Mathis <mathis@rowland.harvard.edu>