* Update Windows registry behavior and canonical 3.15 tests
Add DeleteTree with nullable wide paths, audit emission, native errors, and thread release; compare HKEY handles as CPython does while retaining upstream identity hashing. Migrate canonical winreg and winapi tests from CPython d220409a13b77de7a6c30abe16ea90db01528edc.
Assisted-by: OpenAI Codex: model version unavailable
* Accept nullable subkeys in winreg OpenKey
Keep sub_key required while accepting None, matching CPython and the canonical HKEY comparison test prerequisite. Forward a null path to RegOpenKeyExW, retain owned wide strings across thread release, and emit the input and result audit events without leaking the returned handle on an audit error.
Assisted-by: OpenAI Codex: model version unavailable
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Co-authored-by: Codex <codex@openai.com>
