Mempool preconfs: Cleanup contract_users only after rollback

[Dentosal]

See #3264 (comment)

Description

Problem

on_removed_transaction was called for both block-committed transactions and pool evictions, which meant contract_users entries were cleaned up before rollback_preconfirmed_transaction could use them to find and evict dependent pool transactions.

Solution

Add on_committed_transaction (same as on_removed_transaction but skips the Input::Contract cleanup) and remove_from_contract_users (only the Input::Contract cleanup) to the CollisionManager trait and BasicCollisionManager. Block-commitment paths in pool.rs now use on_committed_transaction and return the removed pool transactions to their callers. pool_worker.rs defers remove_from_contract_users until after all preconfirmation rollback for the relevant block height is complete. This ensures rollback always observes the full set of contract dependents.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

[cursor]

PR Summary

Medium Risk
Changes txpool commit/preconfirmation paths to defer contract_users cleanup, which affects mempool eviction/rollback ordering and could cause stale indexing or missed dependent evictions if the new sequencing is wrong.

Overview
Fixes preconfirmation rollback correctness by splitting collision-manager removal into committed vs evicted paths so contract_users entries remain visible until rollback reconciliation finishes.

Updates the CollisionManager API and BasicCollisionManager to add on_committed_transaction (skips contract_users cleanup) and remove_from_contract_users (does only that cleanup), then changes txpool commit flows to return removed pool txs and have pool_worker perform the deferred cleanup after processing stale preconfirmations for each block height.

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