Saddle Connection Enumeration is slow

[saraedum]

In particular when testing, enumerating saddle connections is very slow. For example, this takes about 13 seconds to complete, see saddle_connection.test.cc:

const auto [name, surface_] = GENERATE(makeSurface<T>());
const auto surface = *surface_;

const auto connection = GENERATE_REF(saddleConnections(surface, 2));
const auto other = GENERATE_REF(saddleConnections(surface, Vertex::source(connection.source(), *surface), 2));