fix(vulture): track the hash_tree_root handler rename

[MegaRedHand]

Problem

The dead-code CI job (just deadcode) fails on main:

src/lean_spec/spec/crypto/merkleization.py:211: unused function '_hash_tree_root_packed_leaf' (60% confidence)
src/lean_spec/spec/crypto/merkleization.py:221: unused function '_hash_tree_root_bytes' (60% confidence)
... (8 handlers total)
error: recipe `deadcode` failed on line 43 with exit code 3

(see https://github.com/leanEthereum/leanSpec/actions/runs/27710866929/job/81971271367)

Cause

The single-dispatch hash_tree_root handlers are registered via @hash_tree_root.register, so their names have no direct call site and vulture cannot see the use. They were whitelisted under the _htr_ prefix.

A later refactor (#1124) renamed them to the spelled-out _hash_tree_root_ prefix but did not update vulture_whitelist.py. The old names no longer exist, so the whitelist entries match nothing and the renamed handlers are reported as unused.

Fix

Rename the eight whitelist entries to match the current handler names. No source code changes.

Verification

• Before: just deadcode fails with the 8 reports above.
• After: just deadcode passes.

[tcoratger]

Thanks!