fix(protocols): re-export what each data and schema submodule exports (#1807)

[JarryShaw]

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Summary

#1797 found pcapkit.protocols.data.link missing the L2TP data model (fixed in #1806). The same gap was open across the data and schema packages: names a submodule lists in __all__ that its package and aggregator did not re-export.

• Re-exported, in each intermediate package and in the data/schema aggregators, under the prefixes the siblings use:
  • the MH messages, options, suboptions, attributes and extensions (MH_*);
  • the HOPOPT and IPv6-Opts SMFDPDOption and QuickStartOption (HOPOPT_*, IPv6_Opts_*);
  • ipv4.Option and ipv6_route.RoutingType on the schema side;
  • PCAP-NG PacketBlock and the PACK_* options (PCAPNG_*);
  • HTTP/2 Settings (HTTPv2_Settings).
• Module-only by design: the schema.internet.ipv6_option field callbacks. No package re-exports field callbacks, the same names exist in sibling modules, and ipv6_option.rst documents them on their own page. They are recorded in the new test's allowlist.
• Guard: tests/protocols/test_package_reexports_1807_unit.py walks every data and schema package and checks re-export by identity, a tight allowlist, and no shadowed star-imports. It fails on main.
• Safety: no name maps to two objects in either aggregator, and pcapkit's own top-level names are unchanged. Additions only.

Closes #1807

[JarryShaw]

Verdict: GOOD TO GO at 7bd02d2f1. A Sonnet cross-review (author: Opus) re-ran the inventory by object identity: every gap is closed and only the justified ipv6_option callbacks remain. It found no star-import clash, and pcapkit's public surface is unchanged (additions only, in data and schema). The new test fails on main, and removing any one re-export fails it where no other test notices. tests/project and the protocol suites pass.

[github-actions]

Coverage: 89.63% (unit tier, Python 3.15, 7bd02d2f1, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	3	20	3	95.16%
pcapkit/const	18862	954	2368	868	91.06%
pcapkit/corekit	2462	69	780	35	96.55%
pcapkit/dumpkit	276	3	100	3	98.40%
pcapkit/foundation	2915	164	1016	34	93.59%
pcapkit/interface	138	7	52	5	93.68%
pcapkit/protocols	17408	224	4580	189	98.10%
pcapkit/toolkit	872	177	298	8	77.18%
pcapkit/utilities	512	2	158	4	99.10%
pcapkit/vendor	4417	2342	1010	157	43.38%

Per-file detail: the coverage-html artifact of this run.