Add fastapi-offline to support offline FastAPI docs

[imClumsyPanda]

Motivation

Add fastapi-offline in cli/fast-api.py to support offline fastapi docs

Modification

add fastapi-offline in cli/fast-api.py and add requirements in pyproject.toml

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

when start minerU-api, docs can be shown in offline environments.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[imClumsyPanda]

I have read the CLA Document and I hereby sign the CLA