Fix UB in LinkedHashMap::clear()

[djc]

Fixes #43.

[Copilot]

Pull request overview

This PR fixes unsound panic-unwind behavior in LinkedHashMap::clear() (Issue #43) by ensuring the value-list guard is left in a consistent empty state even if dropping an entry panics, and adds a regression test to cover the scenario where clear() panics and the panic is caught.

Changes:

• Make drop_value_nodes detach the guard from the value list before dropping any nodes, preventing stale moved-out nodes from remaining reachable after a caught panic.
• Adjust node/entry drop ordering so that, if an entry’s Drop panics, unwinding continues from the next node without revisiting the already-taken entry.
• Add a regression test that catches a panic from clear() and then drops the map to ensure no stale nodes are traversed/dropped again.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/linked_hash_map.rs	Refactors drop_value_nodes to detach the guard first and to be panic-unwind safe during entry drops.
tests/linked_hash_map.rs	Adds a regression test that catches a panic during clear() and validates the map can be safely dropped afterward.

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