- DEFAULT_LIMIT will be changed to 0 in the REST action (separate commit).
- When limit=0 (unlimited), always emit an explicit Limit(Integer.MAX_VALUE)
  so that ESQL's AddImplicitLimit rule sees an existing node and does not
  silently inject its own 1 000-row default with a warning header.
- When limit>0, use limit+1 as a sentinel so the response listener can
  detect truncation: if ESQL returns exactly limit+1 rows the result was
  truncated, a warnings field is added, and the extra row is stripped.
- Update response listener truncation check from size()==limit to
  size()==limit+1, and trim the sentinel row before serialising.
- Update plan-builder and response-listener unit tests accordingly.

Update the class-level plan diagram from [Limit(n)] (which implied the
node was optional) to Limit(limit==0 ? MAX_VALUE : limit+1) to match
the style introduced in the LabelValues plan builder. Also update the
@param limit doc to note that 0 defers to the ESQL max setting.

…LabelsResponseListener