config: scalar top-level JSON returns scalar from array-typed method (TypeError instead of Parse)

[loks0n]

packages/config/src/Config/Parser/JSON.php (~line 30) accepts any valid JSON, but inputs like "foo", 123, or true decode to a scalar and are returned from a method declared : array, causing a TypeError instead of the package's Parse exception.

Fix: check is_array($config) after decoding and throw Parse when the top-level value is not a config map.

Surfaced by Greptile on #25 (config absorption). Pre-existing in the upstream library; filed as follow-up rather than fixed in the absorption PR to keep that change faithful to upstream behavior.