feat: add Mistral Document AI for document parsing

[r-dh]

Adds Mistral as an optional document processor with pip install raglite[mistral-ocr].

Converts PDFs, images, .docx, .pptx, and more to Markdown via Mistral's OCR API. Uses bbox_annotation_format to classify and describe images found in documents, making visual content searchable as text.

Image categories are user-defined, Mistral constrains its classification to whatever types are provided:

RAGLiteConfig(
      document_processor=MistralOCRConfig(
          image_types=frozenset({"chart", "diagram", "photo", "table", "icon", "logo"}),
          exclude_image_types=frozenset({"icon", "logo"}),
      ),
)

Falls back to the default pdftext/pandoc processor for unsupported file types.

Note that this includes a onnxruntime pin for Python 3.10 and a ruff <0.15 cap, the latter which will be resolved in a separate PR.

[emilradix]

@r-dh I marked this as draft, as I understood from your description it is not ready yet to be merged.

[emilradix]

Is this ready for review? In that case you can mark it as ready for review, currently its a draft

[r-dh]

I had to pin ruff to make the tests pass, because the ruff 15.0 release brings a myriad of new linting issues across the repo that should be either addressed in a separate branch, or avoided altogether.

There has also been a new onnxruntime library release in the meantime that is no longer compatible with Python 3.10, so I pinned that as well.

[emilradix]

@MattiaMolon Do you mind reviewing?

@r-dh Can you open a seperate PR that deals with ruff linting for the rest of the repo? Maybe you can let codex run to deal with a lot of those issues?

[MattiaMolon]

Sure, I will review this

[MattiaMolon]

LGTM!
Left 2 small comments for you @r-dh to evaluate if worth changing.

[emilradix]

@r-dh can you update the PR description to be accurate with the current status? Thanks!

[r-dh]

This reminds me I should probably update the README.md as well to reflect these changes. Let me do this first and then update the content of this PR.

[r-dh]

I made one more change so end users can more easily define their own images types that they (don't) want to process.

[emilradix]

@r-dh Please remove the ruff pin and I will merge

[r-dh]

@emilradix Ready to merge