Fix FCU unwind: properly reorg in-memory canonical state and update latest block

[pycckuu]

Fix FCU when new head is an ancestor (unwind). Previously we only updated the header, leaving in-memory canonical state stale, causing tx validation issues (e.g., "nonce too low"). Now we detect unwind, reorg in-memory state (remove old blocks, load ancestor), and keep TreeState and CanonicalInMemoryState in sync.

Code Changes

• tree/mod.rs:
• Add: log_chain_update_type, handle_chain_unwind, collect_blocks_for_removal, apply_canonical_ancestor_via_reorg, handle_chain_advance_or_same_height, ensure_block_in_memory.
• Replace header-only update with:

  self.log_chain_update_type(...);
  self.state.tree_state.set_canonical_head(canonical_header.num_hash());
  if new_head_number < current_head_number {
      self.handle_chain_unwind(current_head_number, canonical_header)
  } else {
      self.handle_chain_advance_or_same_height(canonical_header)
  }

• Reorg on unwind:

  self.canonical_in_memory_state.update_chain(NewCanonicalChain::Reorg { new, old });
  self.canonical_in_memory_state.set_canonical_head(canonical_header.clone());

• Advance/same-height: ensure block committed into memory if missing.
• Interim method update_latest_block_to_canonical_ancestor added, then superseded by full unwind handling.
• tree/tests.rs:
• New test test_fcu_with_canonical_ancestor_updates_latest_block asserting both TreeState and in-memory head match the ancestor after FCU.

Reason for Changes

Correctness: prevent stale in-memory state on reorgs that led to txpool/state provider errors.

Impact of Changes

• Correct state after unwinds; eliminate nonce/state desync errors.
• Low overhead; clearer logging.

Test Plan

• Run: cargo test -p engine_tree test_fcu_with_canonical_ancestor_updates_latest_block.

How the reviewer should test the fix

• Unwind: head=4 → FCU to 2; verify removal of [3,4] and head=2 in both states.
• Advance: head=2 → FCU to 3; verify block 3 committed and head updated.
• Check logs for correct classification.

Other useful info

If ancestor block missing from storage, we warn and still update header to avoid desync.

Closes #17798

[pycckuu]

Closing this PR in favor of a rebase on recent changes #17938