fix: pass flags to v8__ObjectTemplate__SetIndexedPropertyHandler FFI

[popematt]

The FFI declaration for SetIndexedPropertyHandler omitted the flags parameter that the C++ binding accepts, causing any flags set on IndexedPropertyHandlerConfiguration (e.g., NON_MASKING) to be silently discarded. I think it also results in UB because we're calling a C/C++ function with fewer args than expected... and the Rust compiler cannot detect because we correctly called the binding function. The problem is that the extern "C" binding function does not match the actual signature of the C++ function.

The named handler's declaration already passes flags correctly—this aligns the indexed handler to match.

Added a test that sets NON_MASKING on an indexed handler and verifies real indexed elements take priority over the interceptor.

For reference, here is the C++ function that we're trying to match:

rusty_v8/src/binding.cc

Lines 1505 to 1517 in 5d0e31e

	void v8__ObjectTemplate__SetIndexedPropertyHandler(
	const v8::ObjectTemplate& self, v8::IndexedPropertyGetterCallbackV2 getter,
	v8::IndexedPropertySetterCallbackV2 setter,
	v8::IndexedPropertyQueryCallbackV2 query,
	v8::IndexedPropertyDeleterCallbackV2 deleter,
	v8::IndexedPropertyEnumeratorCallback enumerator,
	v8::IndexedPropertyDefinerCallbackV2 definer,
	v8::IndexedPropertyDescriptorCallbackV2 descriptor,
	const v8::Value* data_or_null, v8::PropertyHandlerFlags flags) {
	ptr_to_local(&self)->SetHandler(v8::IndexedPropertyHandlerConfiguration(
	getter, setter, query, deleter, enumerator, definer, descriptor,
	ptr_to_local(data_or_null), flags));
	}

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