Fix _.uniq isSorted fast path failing to deduplicate NaN values

[JSap0914]

Problem

The isSorted fast path in _.uniq uses seen !== computed to detect whether consecutive elements differ. Since NaN !== NaN always evaluates to true per IEEE 754, consecutive NaN values in a sorted array are never recognized as duplicates:

_.uniq([NaN, NaN], true);        // → [NaN, NaN]  (wrong, should be [NaN])
_.uniq([1, NaN, NaN, 2], true);  // → [1, NaN, NaN, 2]  (wrong, should be [1, NaN, 2])

The unsorted path (which delegates to _.contains / _.indexOf) already handles NaN correctly via the NaN branch in createIndexFinder. This bug only affects the isSorted && !iteratee fast path.

Fix

Replace the bare inequality check with a SameValueZero-style comparison that treats NaN as equal to itself:

// before
if (!i || seen !== computed) result.push(value);

// after
if (!i || !(seen === computed || (seen !== seen && computed !== computed))) result.push(value);

The sub-expression (seen !== seen && computed !== computed) is true iff both values are NaN, at which point they are treated as equal and no push occurs.

Tests

Two regression assertions added to the existing uniq test in test/arrays.js. All 208 tests pass.

AI-assisted contribution (GitHub Copilot / Claude).

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