fix(sort): make path comparator consistent for trailing-slash paths

[kistlers]

Fixes #228.

Problem

With sortPathsBy: path, two paths that differ only by a trailing slash (e.g. /pets and /pets/) swap order on every run, so formatting the same document never converges.

sortPathsByAlphabet splits each path on / and uses a truthy !segment test to detect a missing segment. "/pets/".split('/') ends in '' (empty segment) while "/pets".split('/') ends in undefined (no segment) — both falsy. The pathA branch then fires regardless of argument order, so compare(a, b) and compare(b, a) both return -1. That comparator is not antisymmetric, so the sort result depends on the input order and flips between runs.

Fix

Use a strict === undefined check so only a truly absent segment sorts first; an empty trailing-slash segment is compared normally as '' (which sorts before any non-empty segment). The comparator becomes a total order, output is stable across runs, and all other path orderings are unchanged.

-      if (!pathA[i]) return -1;
-      if (!pathB[i]) return 1;
+      if (pathA[i] === undefined) return -1;
+      if (pathB[i] === undefined) return 1;

Tests

Added two unit tests in test/sorting.test.js:

• /pets is ordered before /pets/ regardless of input order (this is the regression: it fails on main for the swapped-input case).
• /pets, /pets/, /pets/{id} keep a stable, sensible order.

Verified the new "regardless of input order" test fails on the current comparator and passes with the fix. Full suite green (npm test: 15 suites, 487 passing), sorting.js at 100% coverage, and prettier --check passes on the changed files.