feat: `parition_pdf()` add ability to get `cid` ratio (#2970)
This PR adds the ability to get the ratio of `cid` characters in
embedded text extracted by `pdfminer`. This PR is the second part of
moving `cid` related code from `unstructured-inference` to
`unstructured` and works together with
https://github.com/Unstructured-IO/unstructured-inference/pull/342.