GeezerVison

What

DocumentsService can only reach IXP projects by name and tag. IXP models that a solution deploys into an Orchestrator folder have their own Document Understanding routes (du_/api/framework/models/{name}/...), and the SDK can't call them. This PR adds:

• extract_with_model(model_name, file | file_path, folder_key=None) (and _async): digitize, extract, and wait for the result.
• ModelExtractionResponse, which carries the model name and the extraction result. Folder models have no project id or tag, and their results have no DataProjection.

The folder routes accept only the X-UiPath-FolderKey header (X-UiPath-FolderPath returns 400 [RequestMissingRequiredField]), so the method takes a folder key and defaults to the current job's folder (UIPATH_FOLDER_KEY). The existing project code is unchanged.

How it was tested

• Unit tests: sync and async, the folder key argument, the current-folder default, an encoded model name, and the error without any folder. The uipath-platform suite, ruff and mypy pass.
• Live run against a tenant with folder-deployed models (invoices-ixp): sync with a folder key and async with UIPATH_FOLDER_KEY both returned all seven field groups.

These routes exist only in Framework API v2, so they always call v2, whatever the DocumentsFrameworkV2 flag says.

Version bumped to 0.2.38, because #1929 takes 0.2.37.