Preserve R6 member providers after inference timeouts

[renkun-ken]

When R6 initializer inference reaches its time limit, completion can retain the declared receiver while signature help and hover return empty results. This caused the macOS failure in R-CMD-check run 38049726953.

Select members directly from the inferred receiver so known declarations survive budget exhaustion. Allow 5 seconds for inference under testthat, retain the normal 250 ms limit and existing 10-second coverage limit, and replace a leaking deep clock stub with a scoped mock.

Validation:

• Regression checks force initializer timeout and verify completion, signature help, and hover without executing user code.
• A simulated 300 ms traversal verifies production timeout enforcement and test tolerance.
• Full macOS R CMD check --as-cran --no-manual: 7,509 passing assertions, zero errors or warnings; one local xcrun_db cleanup note. Used a temporary writable cache and default lint settings to avoid personal configuration interference.
• No new lint findings in changed lines; git diff --check passed.