Sort a base name before its numbered siblings [patch]

[matt-edmondson]

Fixes #61

What changed

When one text chunk was a strict prefix of the other, CompareTextChunks put the shorter chunk first without looking at what came after it. Comparing "file.txt" with "file" + 1 + ".txt" never compared the . against the 1, so report.pdf sorted after report2.pdf.

Now, when the shared prefix matches and the lengths differ:

• if the shorter chunk's string ends there, it comes first, as before;
• otherwise a number follows the shorter chunk, so the comparison uses the longer chunk's next character against that number's first digit, rewritten as ASCII.

This is the order the class remarks promise: "a number compared with text orders exactly as the equivalent ASCII digits would". It also matches the existing mixed text/number branch in Compare. A text chunk never contains a digit, so the two characters always differ. The comparer still allocates nothing.

Tests

• Compare_TextThatExtendsTheOtherSidesText_ComparesItsNextCharacterWithTheNumber covers the acceptance cases (file.txt/file1.txt, file-1/file1, file 2/file10), plus a! against ASCII and Arabic-Indic five, plus guards showing that filea still sorts after file1 and that file still comes before file.txt.
• Sort_PutsABaseNameBeforeItsNumberedSiblings checks that report.pdf sorts before report1/2/10.pdf.
• Compare_IsTransitiveOverMixedScriptDigitsAndText (NaturalStringComparer is intransitive for non-ASCII digits (٥ < 10 < z < ٥), so sort output depends on input order #55) now also includes prefix-shaped values (a!, a.b, a.5, a٥.b, a~, az, a 2, a-1) and stays antisymmetric and transitive.

The two new tests fail on main and pass with the fix. The full suite passes: 27/27.

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https://claude.ai/code/session_011XTgJFveY9S4CJX3Bzeyej

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Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
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100.0% Coverage on New Code
0.0% Duplication on New Code

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