Implement List::copy

[jdolan]

List inherited Object's copy, which memcpy's the instance. For a List that duplicates head, tail and count, so both instances address the same nodes: appending to either corrupts the other's tail, and releasing either frees nodes the survivor still walks. Callers wanting a copy therefore had to build one node by node, as Array's callers have never had to.

Copy as Array does, and as List's own filteredList and mappedList already do: allocate a new List and append each element in order. Elements are not retained, since append does not retain them either, and the copy does not inherit destroy, so it borrows the elements rather than owning them. That is the only safe choice for a container that does not retain, since two owning lists over the same elements would double free.

The test asserts the copy is independent: same elements in the same order, distinct nodes, appending to one leaves the other's count alone, and the original survives the copy's release. It fails on the inherited implementation, on the distinct-nodes assertion.

[Copilot]

🟢 Approval recommended

The change directly addresses the unsafe inherited copy behavior, and it includes a targeted regression test that would fail under the previous implementation.

Pull request overview

This PR fixes List’s copy behavior by overriding Object::copy (which memcpys the instance) with a node-by-node copy that produces an independent list structure, matching the semantics already used by filteredList/mappedList and aligning with how Array::copy returns an independent container.

Changes:

• Override Object::copy for List to allocate a new list and append each element in order (no node sharing).
• Add a new copyList unit test that verifies the copy has distinct nodes, preserves element order, and remains independent after mutation and release.

File summaries

File	Description
Sources/Objectively/List.c	Implements List-specific copy to avoid shared nodes and corruption from the inherited memcpy copy.
Tests/Objectively/List.c	Adds a regression test asserting copied lists are structurally independent and safe to mutate/release.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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