Only send finalState if needed

[taylordowns2000]

Short Description

When a workflow ends with a single leaf step whose dataclip is already persisted, send final_dataclip_id instead of final_state in run:complete to avoid re-uploading state Lightning already has.

Closes #1309 and best served after OpenFn/lightning#4531 is merged.

Implementation Details

• Replaced lastDataclipId with leafDataclipIds[] on RunState, populated in step-complete only for steps with no downstream edges.
• In run-complete, if there's exactly one leaf dataclip that wasn't withheld, send final_dataclip_id; otherwise fall back to sending final_state as before.
• Updated lexicon types, lightning-mock, and tests accordingly.

QA Notes

Branching workflows (multiple leaves) should still send final_state.

• Single-leaf workflows where the dataclip was withheld should also still send final_state.
• Single-leaf, non-withheld workflows should send only final_dataclip_id.

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[josephjclark]

@taylordowns2000 I'm going to put out a worker patch today but I'm going to exclude this as we're waiting on the Lightning PR. I'll get this reviewed properly with a clear head tomorrow.

[taylordowns2000]

that's perfect @josephjclark , thank you! if you do get the chance, a review before Thursday morning (730am Paris time) would be great as it would allow @stuartc and I to review your review when we talk about OpenFn/lightning#4531