fix(foundation): _check_code(number=True) takes a bool, so register_tcp(True) adds port 1 #2269

Describe the bug
_check_code lets any non-enum int through when number=True, and bool is an int subclass. So register_tcp, register_udp and register_sctp store True as key 1.

Reproduction (registries snapshotted and restored)

register_tcp(True, Raw)    # no error
TCP.__proto__.get(1)       # <class 'Raw'>, likewise UDP and SCTP

Expected behavior
RegistryError: code must be an int or a member of AppType, not True, registry unchanged. Suggested fix: reject isinstance(code, bool) before the number branch in _check_code. This is separate from #2268, where the mapping form skips _check_code altogether.

System information
Linux, CPython 3.14.9, pcapkit 1.5.0b14, checkout main 9d504ead5.