register_mh_extension takes schema positionally; the other 14 register_* are keyword-only

[JarryShaw]

Public API inconsistency, one character. Verified by introspecting all fifteen register_* functions in pcapkit/foundation/registry/protocols.py:

register_hip_parameter        schema is KEYWORD_ONLY
register_hopopt_option        schema is KEYWORD_ONLY
register_http_frame           schema is KEYWORD_ONLY
register_ipv4_option          schema is KEYWORD_ONLY
register_ipv6_opts_option     schema is KEYWORD_ONLY
register_ipv6_route_routing   schema is KEYWORD_ONLY
register_mh_extension         schema is POSITIONAL_OR_KEYWORD   <--
register_mh_message           schema is KEYWORD_ONLY
register_mh_option            schema is KEYWORD_ONLY
register_pcapng_block         schema is KEYWORD_ONLY
register_pcapng_option        schema is KEYWORD_ONLY
register_pcapng_record        schema is KEYWORD_ONLY
register_pcapng_secrets       schema is KEYWORD_ONLY
register_tcp_mp_option        schema is KEYWORD_ONLY
register_tcp_option           schema is KEYWORD_ONLY

protocols.py:537-538 is missing the * that its fourteen siblings have.

Widening a parameter to keyword-only is technically breaking for anyone passing it positionally, but the asymmetry is clearly unintended and the prerelease window is the cheap moment to fix it.