chore: dependency updates to resolve cves (#4124)
<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Release 0.18.21 with broad dependency pin updates across requirements
(notably unstructured-inference 1.1.2) to remediate CVEs.
>
> - **Release**
> - Set version to `0.18.21` and update `CHANGELOG.md`.
> - **Dependencies**
> - Upgrade `unstructured-inference` to `1.1.2` in
`requirements/extra-pdf-image.txt` to address CVEs.
> - Refresh pins across `requirements/*.txt` (base, dev, test, and
extras), including updates like `certifi`, `click`, `pypdf`, `pypandoc`,
`paddlepaddle`, `torch`/`torchvision`, `google-auth` stack, `protobuf`,
`safetensors`, etc.; normalize pip-compile headers and constraint paths.
>
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
face075955f8b733f28e17cd26863470b4622def. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
