SVS dynamic indices' add_points()/delete_points() to return number of actually added/deleted vectors.

[rfsaliev]

Dynamic index modification methods behavior should be changed as follow:

• add_points() should allow to override existing vectors (vectors with same labels) and return the number of new vectors only.
• delete_points() should accept non-existing external ids and return the number of vectors which are actually deleted.

ScalableVectorSearch/bindings/c/src/index.hpp

Lines 135 to 151 in ec4260c

	size_t add_points(
	svs::data::ConstSimpleDataView<float> new_points, std::span<const size_t> ids
	) override {
	auto old_size = index.size();
	index.add_points(new_points, ids);
	// TODO: This is a bit of a hack - we should ideally return the number of points
	// actually added, but for now we can just return index size change.
	return index.size() - old_size;
	}
	size_t delete_points(std::span<const size_t> ids) override {
	auto old_size = index.size();
	index.delete_points(ids);
	// TODO: This is a bit of a hack - we should ideally return the number of points
	// actually deleted, but for now we can just return index size change.
	return old_size - index.size();
	}