Achieve 100% line/method coverage; fix fabricated CHANGELOG entry

[Copilot]

The previous session added a CHANGELOG entry claiming a coverage improvement it didn't actually make — MiscCoverageTest.php had already been merged via a prior PR. This branch reverts that entry and does the real work: covering the three genuinely uncovered branches.

New tests (MiscCoverageTest.php)

Test	Target	Trigger
testNestedBlockquoteWithWidthReducesWidth	convertNested line 630 — width -= 2	blockquote with width > 0 option
testPregCallbackUnknownElementReturnsEmpty	pregCallback line 815 — return '' fallback	reflection call with unknown element name
testConvertElementWithNoOptionsReturnsInputUnchanged	convertElement line 939 — return $str fallback	element options overridden to false

The return '' branch in pregCallback and return $str in convertElement are unreachable via normal HTML input, so the former uses reflection and the latter uses an option override:

// line 815 — via reflection
$ref = new \ReflectionMethod($html2text, 'pregCallback');
$ref->setAccessible(true);
$result = $ref->invoke($html2text, ['element' => 'unknownelement', 'value' => 'test']);

// line 939 — options override forces null options for h1
$html2text = new Html2Text('<h1>Hello</h1>', ['elements' => ['h1' => false]]);

Coverage delta

Metric	Before	After
Lines	98.72% (232/235)	100% (235/235)
Methods	82.35% (14/17)	100% (17/17)
Classes	0%	100%

CHANGELOG

Reverted the inaccurate 5.0.5 entry; replaced with an entry that accurately describes only this branch's work.

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This change is