Selected declaration discovery rejects packaged native modules before benchmark preparation #415

Fresh main f2aabe45a84d9834eef37d1862f0d0290ba73b63 cannot prepare the Advanced benchmark with the packaged native granularity extension present. Selected declaration discovery raises:

ImportError: No declaration source for 'openhcs.processing.backends.cellprofiler._granularity_native'

OpenHCSFunctionCatalogDeclaration.discover_source_declarations treats InspectLoader.get_source() == None as an import failure. Native extension and bytecode-only loaders legitimately have no Python source. Source literals are only an eligibility filter; lack of source must retain normal registry discovery so valid sourceless declarations can still register. Actual loader/import failures must continue to propagate.

The failure occurs in prepare_cellprofiler_input_workspace before server startup or pipeline execution. It also causes the existing ExampleHuman and pixel-classification selected-knowledge tests to fail: 52 passed, 2 failed on clean main with the main-declared metaclass-registry gitlink 3294a69dabc9f99dd646c32571b8f97cc139d378.

This is the new selected-discovery boundary introduced by PR #377, related to #376. The older source-decoding bug in #235 was already fixed; this reproducer does not decode a binary as text.

Local evidence: /var/tmp/openhcs-measurement-query-request-capture-20261001/controller.log and /var/tmp/openhcs-latest-main-registry-smoke-corrected-20261001.log.

Acceptance: preserve the native extension, admit sourceless modules through the existing nominal registry, retain source filtering and authoritative import errors, and pass the existing selected-source tests plus a real bytecode-only declaration control. Do not disable the binary, add a second discovery registry, or catch internal imports.