feat: support device scale factor in --viewport

[Aalivexy]

Summary

This PR updates the server CLI --viewport flag to reuse the existing viewport syntax used by emulation tools.

--viewport now accepts both:

• 1280x720
• 1280x720x2

When a device scale factor is provided, it is applied during browser startup in addition to the initial viewport size.

Changes

• add CLI parsing support for <width>x<height>x<deviceScaleFactor>
• preserve the existing <width>x<height> format
• apply deviceScaleFactor during initial browser launch
• update CLI documentation and examples
• add tests for CLI parsing and browser launch behavior

reslove #1140

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[OrKoN]

@Lightning00Blade could you please review?

[Lightning00Blade]

After checking the implementation - I think we can't use this approach as this set the ViewPort only for a single page, which will be reset upon navigation and some other cases as well.

A better approach would be to set the Chrome argument --force-device-scale-factor=X as that will force everything to scale with that factor accordingly.