perf: Use `FxHasher` in more cases

[codecov[bot]]

Codecov Report

Merging #242 (abb069c) into master (8aa0dc4) will decrease coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #242      +/-   ##
==========================================
- Coverage   85.23%   85.21%   -0.02%     
==========================================
  Files          19       19              
  Lines        1612     1610       -2     
==========================================
- Hits         1374     1372       -2     
  Misses        238      238              

Files Changed	Coverage Δ
css-inline/src/html/document.rs	93.44% <100.00%> (ø)
css-inline/src/html/serializer.rs	89.87% <100.00%> (-0.10%)	:arrow_down:
css-inline/src/lib.rs	97.96% <100.00%> (+0.01%)	:arrow_up:

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #242 will not alter performance

_{Comparing dd/more-fx-hasher (abb069c) with master (8aa0dc4)}

Summary

✅ 5 untouched benchmarks