Optimise encodeNonUTF8QueryURLs

[vbanos]

Two optimisations:
We iterate query key -> values and then iterate each value in values. We encoded the key again and again for each value. We only need to do it once. We move the key encoding code outside the values loop.

We define enc.NewEncoder().String() every time we need to encode a value. We can define encoder := enc.NewEncoder() in the beginning and reuse it.

We add a unit test for a bad URL just to be sure.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.39%. Comparing base (0837f4d) to head (2c7ad38).
⚠️ Report is 63 commits behind head on main.

Files with missing lines	Patch %	Lines
...ernal/pkg/postprocessor/extractor/html_document.go	87.50%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #485      +/-   ##
==========================================
- Coverage   56.42%   56.39%   -0.03%     
==========================================
  Files         130      130              
  Lines        8091     8096       +5     
==========================================
+ Hits         4565     4566       +1     
- Misses       3161     3164       +3     
- Partials      365      366       +1     

Flag	Coverage Δ
e2etests	40.65% <68.75%> (-0.01%)	⬇️
unittests	29.37% <68.75%> (-0.01%)	⬇️

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