perf: Simplify iteration over nodes

[Stranger6667]

• [ ] Write a comment about why it is OK + adjust current
• [ ] Recheck boundaries

[codecov[bot]]

Codecov Report

Merging #202 (fc93808) into master (5004947) will decrease coverage by 0.04%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   84.81%   84.77%   -0.04%     
==========================================
  Files          18       18              
  Lines        1343     1340       -3     
==========================================
- Hits         1139     1136       -3     
  Misses        204      204              

Impacted Files	Coverage Δ
css-inline/src/html/document.rs	93.53% <100.00%> (-0.17%)	:arrow_down:
css-inline/src/html/iter.rs	100.00% <100.00%> (ø)
css-inline/src/html/node.rs	81.48% <100.00%> (+1.08%)	:arrow_up: