fix: delegate v3 inference I/O through copick

[uermel]

Tracks #35 and is the second PR in the copick-easymode OME-Zarr 0.5 / Zarr v3 migration stack.

This keeps volume ownership in copick and proves the handoff with real local copick entities:

• equivalent numeric/nonnumeric OME-Zarr 0.4 / Zarr v2 and OME-Zarr 0.5 / Zarr v3 inputs;
• canonical core-writer and noncanonical gzip/chunk layouts;
• identical model inputs, exact threshold semantics, and uint8 output;
• OME-Zarr 0.5 / Zarr v3 output validation through the public OME model;
• consistent sanitized copick identities while preserving raw easymode model lookup;
• exist_ok=True entity reuse for working overwrite behavior;
• skip-before-read and v2/v3 failed-inference preservation contracts; and
• model/run failure continuation, config-save timing, and unconditional runtime cleanup.

Validation: 31 tests pass against the published copick==2.0.0a1 environment.

No direct Zarr/OME storage code is added to the package runtime, and no release or publication work is included.