Release every persistent V8 handle before isolate teardown #851

Problem

The exact Linux package gate crashes in many otherwise independent V8 test executables during runtime destruction. GDB from run 35511487622 identifies a stale persistent handle released after its isolate:

v8::internal::GlobalHandles::NodeSpace<...>::Release
webscene_native::v8_dom_runtime::implementation::~implementation()
v8_dom_runtime::~v8_dom_runtime()
webscene_engine::run_core

implementation::~implementation() disposes its owned isolate inside the destructor body, but several v8::Global owners remain populated and are therefore destroyed later with the C++ object. The generated meter/output/progress element templates are direct omissions. Active drag state, outbound drag state, and the discrete wheel animation can also retain persistent handles across teardown.

Proposed fix

• Release every direct generated DOM template before isolate disposal.
• Reset optional/owned interaction state that contains v8::Global handles before isolate disposal.
• Keep async worker shutdown and handle release ordered before Isolate::Dispose().
• Audit every direct and nested persistent handle owner in runtime state against the destructor.

Acceptance

• Focused native V8 runtime tests exit normally on Linux without GlobalHandles::NodeSpace::Release faults.
• The exact package gate has no teardown SIGSEGV across independent V8 executables.
• Shared-isolate and owned-isolate lifetimes both retain their existing order.
• No additional steady-state work or memory is introduced.

Evidence

• Exact package run: https://github.com/SceneTech/WebScene/actions/runs/35511487622
• Linux job: https://github.com/SceneTech/WebScene/actions/runs/35511487622/job/106080267370

Parent tracker: #687