Publish reproducible PharmaPy documentation

[bernalde]

Summary

• define a reusable docs dependency extra and install it from Read the Docs and GitHub Actions
• make the complete Sphinx site build reproducibly with warnings treated as errors, including notebooks and their Pandoc/image requirements
• preserve the original PharmaPy credits while adding the current developers, maintainers, and joint-project partners
• update package metadata, installation links, and the CI badge for PharmaPy-org/PharmaPy

Verification

• sphinx-build -E -a -W --keep-going -b html doc/online_docs /tmp/pharmapy-docs-130-site
• actionlint .github/workflows/docs.yml .github/workflows/ci.yml
• python -m pip check in a fresh Python 3.11 docs environment installed with .[docs]
• python -m compileall -q PharmaPy
• python -m pytest tests/ -m "not assimulo" (56 passed, 14 deselected)

Read the Docs follow-up

This PR makes the repository build-ready, but it intentionally does not close the issue. An administrator of the existing Read the Docs project must reconnect it to PharmaPy-org/PharmaPy and verify the live site, webhook, and pull-request previews. If that project cannot be transferred, issue #130 documents the fallback import procedure.

Refs #130

[bernalde]

Review requested from the full current team. GitHub has formally notified the active non-author members.

@ZacharyHillman18 @Piyush1698 @QHuckaba — your PharmaPy-org and repository invitations are still pending, so GitHub cannot add you as formal requested reviewers yet. Please accept those invitations and review this PR; after acceptance, you can also be added to the formal reviewer list.