Fix potential use-after-free for v8 isolates

[stroiman]

When a V8 ScriptHost is closed, it is returned to a pool of isolates, optimizing construction of new isolates. However is code holds on to the ScriptHost, it could lead to a use-after-free bug.

Consider returning a proxy, whose implementation pointer is reset to nil after closing.

Same issue could be applied to other script engines, if they cache script hosts.

[coderabbitai]

Related Issues

• Recycle unused v8 isolates #31: Recycle unused v8 isolates

Suggested Issue Assignees

• stroiman

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