Consolidate `mdbook` version

[nerdai]

The ai-pocket-ref books use a custom theme that was derived from mdbook v0.4.44. However, our preprocessors were built against mdbook v0.4.47. We should update our custom them to this latest version. And then also update the CONTRIBUTING.md as well as the Github action for publishing.

[nerdai]

CI/CD gives us this nice warning that emnates from our mdbook-github-authors and mdbook-ai-pocket-reference preprocessors:

Run mdbook build books/nlp
2025-03-11 17:25:49 [INFO] (mdbook::book): Book building has started
Warning: The mdbook-github-authors preprocessor was built against version 0.4.47 of mdbook, but we're being called from version 0.4.44
Warning: The mdbook-ai-pocket-reference preprocessor was built against version 0.4.47 of mdbook, but we're being called from version 0.4.44
2025-03-[11](https://github.com/VectorInstitute/ai-pocket-reference/actions/runs/13794336451/job/38582102135#step:6:12) 17:25:49 [INFO] (mdbook::book): Running the html backend
2025-03-11 17:25:49 [INFO] (mdbook::book): Book building has started
Warning: The mdbook-github-authors preprocessor was built against version 0.4.47 of mdbook, but we're being called from version 0.4.44
Warning: The mdbook-ai-pocket-reference preprocessor was built against version 0.4.47 of mdbook, but we're being called from version 0.4.44
2025-03-11 17:25:49 [INFO] (mdbook::book): Running the html backend
2025-03-11 17:25:49 [INFO] (mdbook::book): Book building has started
Warning: The mdbook-github-authors preprocessor was built against version 0.4.47 of mdbook, but we're being called from version 0.4.44
Warning: The mdbook-ai-pocket-reference preprocessor was built against version 0.4.47 of mdbook, but we're being called from version 0.4.44
2025-03-11 [17](https://github.com/VectorInstitute/ai-pocket-reference/actions/runs/13794336451/job/38582102135#step:6:18):25:49 [INFO] (mdbook::book): Running the html backend