fix(ocr): make the OCR render scale configurable instead of hardcoded

[Anai-Guo]

Fixes #3866

Problem

Every local OCR engine hardcoded its render scale:

self.scale = 3  # multiplier for 72 dpi == 216 dpi.

so pages are always upscaled to 216 DPI before being handed to the OCR engine. As reported in #3866, that is the wrong default for sources that are already high resolution: the reporter's clean flattened-acroform image OCR'd correctly with tesseract directly, but produced errors through Docling — and the errors disappeared when the temp image was not enlarged. There was no way to change this short of editing the model class.

Change

Add a scale field to the shared OcrOptions base and have the engines read self.options.scale instead of the literal:

• EasyOcrModel
• RapidOcrModel
• OcrMacModel
• NemotronOcrModel
• TesseractOcrModel (tesserocr)
• TesseractOcrCliModel

The default is 3.0, so behaviour is unchanged for anyone who does not set it. gt=0.0 rejects a zero/negative scale at validation time.

This follows the pattern already used elsewhere in the codebase — KserveV2OcrOptions.scale and PictureDescriptionBaseOptions.scale are both configurable float multipliers. KserveV2OcrOptions keeps its own 2.0 default via the existing override.

converter = DocumentConverter(
    format_options={
        InputFormat.IMAGE: ImageFormatOption(
            pipeline_options=PdfPipelineOptions(
                do_ocr=True,
                ocr_options=TesseractCliOcrOptions(scale=1.0),  # no upscaling
            )
        )
    }
)

The one non-mechanical edit is NemotronOcrModel._to_bounding_rect, whose scale: int parameter annotation becomes scale: float so ty stays happy.

Verification

• ruff@0.15.12 check / format --check clean on the changed files (pinned pre-commit version).
• Added test_ocr_scale_is_configurable in tests/test_options.py, which asserts the default stays 3.0, that a custom scale reaches the model instance, and that scale=0 is rejected. Run against a local build:

tesseract model.scale = 1.0
easyocr model.scale = 1.5
default model.scale = 3.0
OK: scale=0 rejected

A dynamic "figure out the effective resolution automatically" heuristic — the reporter's stretch suggestion — is deliberately left out of scope here; this PR only removes the hardcode.

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