Improve fuzzy search scoring: fix IsAcronymNumber bug, take max(acronym, fuzzy), proportional length bonus

[Copilot]

The fuzzy score algorithm produced counterintuitive rankings: short queries like "at" ranked "Kate" above "ATLauncher" (consecutive match scored higher than the acronym), and same-prefix strings of different lengths (e.g. "VLC" vs "VLC media player") received undifferentiated scores.

Changes

Bug fix: IsAcronymNumber always returned false

// Before: compares char to int literals 0 and 9 (NUL/HT control chars) — always false for digits
=> stringToCompare[compareStringIndex] >= 0 && stringToCompare[compareStringIndex] <= 9;

// After
=> stringToCompare[compareStringIndex] >= '0' && stringToCompare[compareStringIndex] <= '9';

Take max(acronym_score, fuzzy_score) when both paths complete

Previously, a successful acronym match short-circuited the fuzzy score entirely. For "at" vs "ATLauncher", the acronym score was 66 (2/3 acronyms matched) while the fuzzy consecutive score is 99 — but only the acronym score was returned, losing to "Kate"'s fuzzy score of 90. Now both scores are computed and the higher is returned.

Replace step-function length bonus with a continuous proportional formula

// Before: coarse step function
if (stringToCompare.Length - query.Length < 5)  score += 20;
else if (stringToCompare.Length - query.Length < 10) score += 10;

// After: continuous — rewards queries that cover a larger fraction of the result string
score += (int)((double)query.Length * 20 / stringToCompare.Length);

This creates a proper gradient so "vlc" ranks "VLC" (score 130) above "VLC media player" (113) above "VLC settings shortcut" (112) rather than treating them equally.

Test updates

• Benchmark scores in WhenGivenQueryString_ThenShouldReturn_TheDesiredScoring updated (all changes ≤ 5 points).
• Two new ordering tests added: WhenQueryMatchesAtStartVsMiddle_ShouldRankStartHigher and WhenQueryCoversMoreOfString_ShouldScoreHigher.

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