Verify delegated converters and processors across Zarr formats

[uermel]

Parent epic: #84

Implementation: #96, stacked on #93

Goal

Verify that representative copick-utils converters and processors keep their decoded behavior while new three-dimensional storage remains delegated to the copick core writer.

Implemented scope

• Exercise real local Copick filesystem entities rather than storage mocks.
• Verify utility tomogram and segmentation writers produce OME-Zarr 0.5 / Zarr v3 through core.
• Verify a representative rescale processor delegates its read/write path.
• Verify a core writer failure remains present in the existing lazy-worker errors result.
• Keep command partial-failure exit semantics unchanged.

There is no source-parsing test for a second writer. The absence of duplicate metadata/codec/chunk/shard policy is enforced through review, while tests validate the actual delegated output behavior.

Acceptance criteria

• Representative new tomogram and segmentation outputs are canonical Zarr v3 artifacts.
• Processor output remains semantically correct.
• Writer failures are not swallowed.
• No independent utility writer is introduced during review.
• test: verify delegated canonical writers #96 passes and merges after feat: resolve tomogram levels from OME metadata #93.