docs: the API docs build prints Sphinx warnings for ambiguous cross-references, an unresolved forward reference and an orphan footnote #2743

Describe the bug
The HTML docs build of main (ab7be2fb0) succeeds but prints six Sphinx warnings. They appear the same with sphinx-autodoc-typehints 3.17.2 and 3.17.4, so they come from our sources, not from the #2742 bump.

Reproduction
Build docs/ in a clean venv from docs/requirements.txt, using the sphinx-build -b html command that make -C docs html runs. The warnings are:

• IGMP._dispatch: the forward reference Raw in its annotations cannot be resolved (sphinx_autodoc_typehints.forward_reference).
• docs/source/pcapkit/protocols/link/netlink.rst: footnote [*] is never referenced.
• DTLS class docstring: Protocol resolves to both pcapkit.protocols.protocol.Protocol and pcapkit.protocols.data.protocol.Protocol.
• TransType, location <unknown>: resolves to both the const and the vendor class.
• HandshakeType, location <unknown>: resolves to the SSLv2 and TLS classes under both const and vendor.
• Query.checksum in pcapkit.protocols.schema.internet.igmpv3: Checksum resolves to both const.tcp and vendor.tcp.

Expected behavior
A clean build: each cross-reference names its target in full, and nothing is left unresolved or orphaned. #709 fixed this same kind of ambiguity before.

System information
Linux, CPython 3.15.2, Sphinx 9.2.0, checkout ab7be2fb0.