🐛 Preserve QDMI provider lifetime and target metadata

[burgholzer]

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Description

Fix QDMI metadata and provider ownership defects found in the follow-up audit:

• Preserve explicit ordered Qiskit placements for fixed-arity gates, including CCX, and convert raw QDMI durations to seconds. For example, duration 20 with unit ns and scale 0.5 now becomes 10 ns rather than 20 seconds.
• Share providers by loaded module and symbol prefix, retain them across fresh sessions, accept setup warning statuses, and reject null session/child handles with cleanup.
• Contain configuration exceptions at session allocation, return NOTSUPPORTED for valid custom session enums, reject embedded NULs in SC names, and reuse topology sets during override validation.

Consolidate redundant Python semantic tests while retaining binding coverage, and isolate registration tests so invalid providers cannot contaminate later enumeration.

Includes independent lifetime/session fixes from #2230 and allocation/enum fixes from #2229. The remaining driver redesign stays deferred. No independent extraction from #2231 was justified because its shared-client and staging changes depend on that redesign. This PR has no dependency on those PRs.

Validation: 465 native QDMI tests passed, one existing SC test skipped; 10 staging/configuration checks passed; 468 serial Python QDMI/plugin tests passed. Repository lint passed. Committed-diff C++ lint checked all six changed C++ source files with zero findings. Hosted CI is pending. These changes concern unreleased v4 functionality, so no standalone changelog or upgrade entry is required.

Codex assisted with the audit, implementation, tests, and this description. Human review remains pending.

Checklist

• The pull request only contains commits that are focused and relevant to this change.
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[codecov]

Codecov Report

❌ Patch coverage is 96.55172% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/qdmi/driver/Driver.cpp	95.0%	4 Missing ⚠️

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[burgholzer]

Another batch of nice improvements. Some of them pulled out of the 4.1 PR stack already, which should help to trim these down.