Add output url to image diff renderer

[frankdekker]

Adds PHPUNIT_EXTENSIONS_IMAGE_DIFF_OUTPUT_URL to the ImageDiffRenderer to optionally set a url where the rendered diff will be available.

[Copilot]

Pull Request Overview

This PR adds optional URL configuration for the image diff renderer to improve user experience when running tests in CI environments. Instead of showing a local file path, users can now configure a web-accessible URL where the diff HTML file can be viewed.

• Introduces PHPUNIT_EXTENSIONS_IMAGE_DIFF_OUTPUT_URL environment variable support
• Modifies the constructor to accept and process an optional output URL parameter
• Updates the render method to use the configured URL when available instead of the local path

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Renderer/ImageDiffRenderer.php	Adds outputUrl property and constructor parameter, implements URL-based diff viewing
tests/Unit/Renderer/ImageDiffRendererTest.php	Adds test case to verify URL-based rendering functionality
README.md	Documents the new PHPUNIT_EXTENSIONS_IMAGE_DIFF_OUTPUT_URL environment variable

Comments suppressed due to low confidence (1)

tests/Unit/Renderer/ImageDiffRendererTest.php:63

• The test method name 'testRenderShouldWithOutputUrl' is grammatically incorrect. Consider renaming it to 'testRenderShouldUseOutputUrl' or 'testRenderWithOutputUrl' for clarity.

    public function testRenderShouldWithOutputUrl(): void