Summary

• Add NAPI test coverage for handle scopes, references, and exception handling
• Fix two bugs discovered by the new tests

New tests

Handle scopes (handle_scope.rs + handle_scope_test.js):

• napi_open/close_handle_scope
• napi_open/close_escapable_handle_scope + napi_escape_handle
• Nested handle scopes
• Double escape detection

References (reference.rs + reference_test.js):

• napi_create_reference with strong refcount
• napi_get_reference_value / napi_delete_reference
• napi_reference_ref / napi_reference_unref counting
• napi_create_external / napi_get_value_external roundtrip
• External values accessed through references

Exceptions (exception.rs + exception_test.js):

• napi_is_exception_pending
• napi_get_and_clear_last_exception
• Exception propagation through napi_call_function

Bug fixes

napi_escape_handle double-call panic: The escapable handle scope was
a complete no-op with no state tracking. Calling napi_escape_handle
twice would silently succeed instead of returning
napi_escape_called_twice. Fixed by tracking escape state via a
heap-allocated bool created in napi_open_escapable_handle_scope.

napi_throw + napi_get_and_clear_last_exception cycle broken:
napi_throw was both storing the exception in env.last_exception AND
calling scope.throw_exception(). This made it impossible to clear the
exception with napi_get_and_clear_last_exception since V8 still had a
pending exception. Fixed by only storing in env.last_exception; the
callback wrapper (call_fn) already handles the V8 throw after the
callback returns.

Test plan

• ./x test-napi passes: 72 passed, 0 failed

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