📦 Reassess and remove spdlog after neutral-atom extraction

[burgholzer]

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Goal

After the neutral-atom stack moves to QMAP, reassess whether the small amount of remaining QDMI diagnostic output justifies retaining spdlog as a Core dependency and package requirement.

Scope

• Refresh all remaining logging call sites after the NA extraction.
• If only simple diagnostics remain, replace spdlog with a small internal diagnostic callback or existing facility.
• Remove unconditional package discovery, FetchContent, install rules, cache options, and shared/static packaging workarounds associated with spdlog.
• Preserve actionable diagnostics and avoid introducing a new public logging abstraction without a demonstrated consumer.

Acceptance criteria

• Either spdlog has a documented remaining justification or it is fully absent from Core's build and installed package.
• Provider and driver diagnostics remain testable and useful.
• Shared/static installs and wheels contain no stale dependency artifacts.