starknet_patricia: extract finalize_binary_child helper from node_from_binary_data

[yoavGrs]

Replace the two-iteration for loop with two calls to a new finalize_binary_child
helper, and collapse the let-else + re-match into a single direct match on the child.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

[reviewable-StarkWare]

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[yoavGrs]

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• starknet_patricia: assert unmodified-subtree binary child is present in the skeleton #14614
• starknet_patricia: extract finalize_binary_child helper from node_from_binary_data #14613 👈 (View in Graphite)
• starknet_patricia: thread the leaf output map separately from LeafSource #14600
• starknet_patricia: collapse leaf handling to a single match #14583
• starknet_patricia: introduce LeafSource enum for filled-tree leaf handling #14582
• main

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PR Summary

Low Risk
Mechanical refactor inside Patricia skeleton tree construction; logic is preserved with the same insert/assert paths.

Overview
Refactors node_from_binary_data when both children are non-empty: the inlined loop that finalized each child into the updated skeleton is replaced with two calls to a new private helper finalize_binary_child.

The helper uses a single match on TempSkeletonNode to map original binary/edge children to UpdatedSkeletonNode inserts, while leaves and unmodified subtrees still only get assertions or early returns (unchanged semantics).

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[nimrod-starkware]

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Reviewable status: complete! all files reviewed, all discussions resolved (waiting on yoavGrs).