starknet_patricia: thread the leaf output map separately from LeafSource

[yoavGrs]

Move leaf_index_to_leaf_output out of the LeafSource::ComputeLeaves variant and
pass it to compute_filled_tree_rec as its own Arc, mirroring filled_tree_output_map.
This lets create reclaim the leaf output map via the existing
remove_arc_mutex_and_option_from_output_map helper instead of unwrapping the shared
LeafSource Arc and matching a single variant with an unreachable! arm.

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

[reviewable-StarkWare]

This change is 

[yoavGrs]

• 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
• starknet_patricia: thread the leaf output map separately from LeafSource #14600 👈 (View in Graphite)
• 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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[cursor]

PR Summary

Low Risk
Internal Patricia Merkle tree fill/refactor with unchanged public API; behavior should match prior Arc-reclaim logic with simpler teardown.

Overview
Refactors how computed leaf outputs are collected after FilledTreeImpl::create finishes the parallel fill.

LeafSource::ComputeLeaves now holds leaf_index_to_leaf_output as an Arc<HashMap<…>>, and create builds that map once, clones the Arc into the leaf source (same pattern as filled_tree_output_map). After compute_filled_tree_rec completes, it drop(leaf_source) so the caller’s Arc to the leaf output map can be reclaimed instead of Arc::into_inner on LeafSource plus a ComputeLeaves-only match with an unreachable! arm.

The duplicate remove_mutex_and_option_from_output_map helper is removed; leaf outputs are finalized with the existing remove_arc_mutex_and_option_from_output_map path used for the filled tree map.

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[nimrod-starkware]

@nimrod-starkware reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on yoavGrs).

[gkaempfer]

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