Clean up run loop shutdown callbacks

[satoshi-assistant]

Summary

• unregister platform run loop timers, sources, and queued callbacks during shutdown
• avoid retaining RunLoopInner from scheduled callback handles by using weak references
• add shutdown coverage for detached scheduled callbacks

Verification

• cargo test -p novonotes_run_loop -p run_loop_timer
• cargo clippy -p novonotes_run_loop -p run_loop_timer --all-targets -- -D warnings
• cargo test --workspace
• novonotes-products with local Cargo patch: cargo check -p pulsus_engine --all-targets
• novonotes-products with local Cargo patch: cargo test -p wrac_log

Note: cargo clippy --workspace --all-targets -- -D warnings still fails on existing wry deprecated/unused-unsafe warnings unrelated to this change.