[hakarrr]

Fixes #640.

Both deepcopy implementations copied values but reused the original keys. For a custom hashable object used as both a key and a value, this retained a reference to the original key and broke the key/value alias in the copy.

Deep-copy keys with the same memo used for values, matching dict deepcopy behavior. Two regression methods cover wrapped/unwrapped BaseDict instances, frozen instances, key/value aliases, mutation independence, and benedict's custom keypath/keyattr settings. Cyclic mapping rejection is unchanged.

Validation on Linux:

• Untouched main: 990 tests pass in a credential-free environment.
• New regression on unchanged production code: all 8 subtests fail.
• Final code: all 992 tests pass on CPython 3.11.17 and 3.12.15.
• Python 3.12 combined line/branch coverage: 98%.
• All pre-commit hooks pass, including Ruff and mypy. Standalone mypy passes all 65 source files on both baseline and final code.
• Wheel/sdist builds and diff whitespace check pass.

Real S3 integration tests use their existing no-credentials early-return path, as on upstream CI; mocked S3 tests still run. Real AWS operations were not verified. Python 3.13-3.15, PyPy, and other operating systems were not run. No existing tests or CI configuration were changed.