fix(removeDimensions): only remove dimensions from the top-most <svg>

[abhu85]

Problem

Fixes #2217.

removeDimensions strips width/height from every <svg> element, including nested ones:

<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10" viewBox="0 0 10 10">
  <path fill="pink" d="M0 0h10v10H0Z"/>
  <svg x="1" y="1" width="8" height="8" viewBox="0 0 33 33">
    <path fill="red" d="..."/>
  </svg>
</svg>

Today the nested <svg> loses width="8" height="8", which changes how it is sized and positioned — the rendered output is visibly different. The plugin docs say it should only affect "the top-most <svg> element", so this is a behavior/doc mismatch.

Fix

Gate the visitor on parentNode.type === 'root' so only the outermost <svg> is touched — the same root-detection other plugins already use (removeOffCanvasPaths, reusePaths, addAttributesToSVGElement; removeViewBox uses the inverse to handle nested <svg>). Nested <svg> dimensions are now preserved.

Test plan

• Added fixture test/plugins/removeDimensions.06.svg.txt: outer <svg> drops width/height, nested <svg> keeps them.
• New fixture fails on main (nested dims stripped) and passes with the fix.
• Existing removeDimensions.01–.05 unchanged; full plugin fixture suite 370 passing.
• eslint + prettier --check clean.