Stop emitting names Lightning rejects

sanitize_name("‍", unicode_mode=True) returns a name made entirely of a zero-width joiner, which Lightning refuses. And a hundred ZWJ families is 100 graphemes but 700 codepoints, against Lightning's 255-codepoint column, so we would emit a name Lightning rejects. The grapheme cap bounds neither.

This is what gates APOLLO_UNICODE_STEP_NAMES.

Two smaller things while we are in here. The parametrizations at test_name_rules.py:353-362 do del expected and then assert a property derived from the function under test, so they survive replacing _fallback_clusters with lambda t: list(t). And the root conftest.py network guard blocks socket.socket.connect but not create_connection or getaddrinfo.

The other items this issue used to carry are resolved in #658.