Retain job realms and trace module lifetimes

[undy-aeon]

Queued jobs keep their arguments alive, but currently do not retain their realm. If the last external context reference is released while a job is pending, executing that job can access a freed context. Top-level-await state can likewise keep a module reachable after its context's loaded-module list is destroyed, causing a use-after-free during runtime teardown.

This ports and adapts bellard/quickjs@458c34d:

• retain a job's realm until execution or runtime teardown
• make module definitions GC-traced objects so asynchronous module state can outlive its context safely
• add regressions for a queued job after external context release and for repeated dynamic imports through a pending top-level-await dependency

This is the focused lifetime item still listed in #1166.

Validation:

• ASan and warnings-as-errors build and API tests
• ASan GC-stress API tests
• UBSan and warnings-as-errors build and API tests
• make ctest cxxtest with both NaN-boxing modes
• test262 configuration: 0/117 errors, 9 excluded