[New] Support saving images separately

[adombeck]

Description

The HTML log file can become very large and take a long time to load. This PR allows saving images separately and load them on demand.

log_image() can now save images separately and reference them by relative URL instead of embedding them as inline base64. This reduces the overall file sizes, because base64 is 33% larger than binary, and it keeps the HTML log small and lets the browser load images on demand rather than parsing megabytes of inline base64.

The feature is opt-in: set the Robot Framework variable ${YARF_IMAGE_DIR} to the directory where images should be saved. When the variable is not set, log_image() falls back to inline base64 embedding as before.

Documentation

The new ${YARF_IMAGE_DIR} variable is documented in the docstring of log_image().

Tests

We've been using this patch for some weeks/months now and didn't experience any issues. It reduces the size of the log.html file from > 100 MB to ~6 MB and allows it to be opened within a second instead of over 10 seconds.

Test cases were added.

[Copilot]

Pull request overview

Adds opt-in image file saving to log_image() in the Robot Framework image utility. When ${YARF_IMAGE_DIR} is set, images are saved as WebP files and referenced by relative URL (from ${OUTPUT_DIR}), keeping log.html small. When unset, behavior is unchanged (inline base64 WebP).

Changes:

• New _get_images_dir() helper that reads ${YARF_IMAGE_DIR} via BuiltIn() and ensures the directory exists, handling RobotNotRunningError.
• log_image() branches: save WebP to disk with a UUID filename and emit a relative <img src="..."> (relative to ${OUTPUT_DIR} when available, otherwise absolute), or fall back to the existing inline base64 path.
• Unit tests for the new helper, the file-saving path (with and without ${OUTPUT_DIR}), and the base64 fallback path.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
yarf/rf_libraries/libraries/image/utils.py	Adds _get_images_dir() and the file-saving branch in log_image().
yarf/rf_libraries/libraries/image/tests/test_utils.py	Adds tests covering the new directory helper and both log_image branches.

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