`compileChildrenPattern` re-implemented the delimiter-list compile
inline with two divergences from the shared
`CompileDelimiterListPattern`:
- It never stripped backticks, so a backtick-wrapped
`children_delimiter` like `` `###` `` matched the **literal wrapped
token** rather than the inner `###`.
- It sorted by **byte length** instead of rune count (`sortSlice`), so
multi-byte delimiters could be ordered incorrectly and a longer
delimiter could fail to win over a shorter prefix.