Memgraph 3.13.0 ships thirteen breaking Cypher semantics changes in one release

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The same 2026-09-09 release changes results silently for existing queries: size()/substring()/left()/right() count characters not bytes so size('中') is 1 not 3, numbers starting with 0 are octal so 09 is now a parse error, a RETURN inside EXISTS{} now affects the answer, single() returns null instead of true when the predicate is null for any element, split('',...) returns [''] not [], and a bare CALL{} subquery no longer leaks outer variables into unimported patterns. --metrics-format also defaults to OpenMetrics instead of JSON, so unset deployments serve a different endpoint format after upgrade. Most of these change results with no error raised, which makes this a read-the-notes-first upgrade.