parseColonPath split the anchor asymmetrically (root trimmed the delimiter
colon as part of a literal "/root:" prefix, item cut on it), and the root
branch's comment talked about the driveID which isn't this function's
concern. Split once at the first colon into anchor + rest, then classify
the anchor (exactly "/root", or "/items/{id}" with a single-segment id).
Same behavior, easier to follow.
Also add explicit coverage for the rule that a suffix requires a second
colon: "/root:/Documents/children" (no second colon) is the path
"/Documents/children", not the path "/Documents" with a "/children"
suffix. Two tests pin it end-to-end - it must route to the bare item (not
/items/{id}/children) and Stat must receive the full path.
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