feat(plugin-markdown-image): allow 'strict' in size

[Mister-Hope]

This PR allow setting 'strict' with size and fixes some wrong documentation introduced by #449. cc @LincZero

[Copilot]

Pull Request Overview

This PR updates the markdown image plugin to allow a new 'strict' mode for the size option while also fixing related documentation errors.

• Updated the TypeScript interface in options.ts to support size as boolean or 'strict'.
• Adjusted the plugin logic to pass additional configuration when size is 'strict'.
• Revised the documentation in both Chinese and English to clarify the behavior of size and legacy size configurations.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
plugins/markdown/plugin-markdown-image/src/node/options.ts	Updated the type definition for the size option.
plugins/markdown/plugin-markdown-image/src/node/markdownImagePlugin.ts	Modified logic to use the imgSize plugin with strict mode option.
docs/zh/plugins/markdown/markdown-image.md	Revised documentation to explain size and legacySize options in Chinese.
docs/plugins/markdown/markdown-image.md	Revised documentation to explain size and legacy configuration in English.

Comments suppressed due to low confidence (1)

docs/plugins/markdown/markdown-image.md:113

• The English documentation references 'legacy: true', but the plugin code uses the 'legacySize' option. Please update the documentation to 'legacySize: true' for consistency.

You can use `=widthxheight` to specify the image size at the end of the link when setting legacy: true in plugin options.