fix(workflow): report truncated=True when _truncate_array drops or shortens array elements

[lalala223]

Fixes #37192

Summary

VariableTruncator._truncate_array could return truncated=False even though array data was actually dropped or shortened, in two cases:

1. Size-limit break drops elements without flagging it — when the running size exceeds the budget the loop breaks and discards the remaining elements, but truncated was left unset. The element-count-limit branch a few lines above already returns True in the same situation.
2. The per-element flag was overwritten instead of accumulated — so an element that fit after a truncated one reset an earlier True back to False.

The fix mirrors the existing correct pattern in the sibling methods truncate_variable_mapping and _truncate_object, which accumulate the flag.

The flag funnels into inputs_truncated/outputs_truncated on the streaming node events, so a false negative reports truncated node values as untruncated. Impact is minor/cosmetic — the final workflow_finished output is not truncated and no data is lost.

Screenshots

Same input ({"result": [10, 20, 30, 40, 50]}, small WORKFLOW_VARIABLE_TRUNCATION_MAX_SIZE), node_finished event:

Before	After
"outputs":{"result":[10]}, "outputs_truncated":false	"outputs":{"result":[10]}, "outputs_truncated":true

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods