Preserve non-breaking spaces during whitespace collapsing

[Copilot]

Default minification was collapsing literal non-breaking spaces as if they were ordinary whitespace, which could erase meaningful content such as  -backed spacing. This change keeps non-breaking spaces intact while still compacting regular collapsible whitespace.

• Regression coverage

  • Add a focused PHPUnit case for the default new HtmlMin()->minify($html) path where a literal NBSP-separated text node must survive minification unchanged.

• Whitespace collapsing

  • Narrow the whitespace-compaction regex to HTML ASCII whitespace (space, tab, form feed, CR, LF) instead of Unicode [:space:].
  • Preserve U+00A0 /   in text nodes while retaining existing whitespace normalization behavior for normal collapsible whitespace.

• Behavioral example

  $htmlMin = new HtmlMin();
  $nbsp = html_entity_decode(' ', ENT_QUOTES | ENT_HTML5, 'UTF-8');
  
  $html = '<span>' . $nbsp . ' ' . $nbsp . '</span>';
  
  echo $htmlMin->minify($html);
  // Before: <span></span>
  // After:  <span>   </span>

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This change is 

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[voku]

Fix #136

[coveralls]

coverage: 95.727%. remained the same — copilot/fix-preserve-nbsp-character into master