fix(protocols)!: make NTPTimestamp and PMIPv6Timestamp Info classes (#1886)

[JarryShaw]

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• Added a changelog entry under docs/source/changelog/ and regenerated CHANGELOG.md, if the change is user-visible: N/A — centralised in docs(changelog): shared 1.5.0 changelog — long-lived, merges last (#610, #616, #617, #618, #620) #657

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As ruled on #1869, NTPTimestamp and PMIPv6Timestamp become Info classes. Breaking: NTPTimestamp shipped as a tuple in every 1.4.x release.

• New home. Both move to pcapkit/protocols/data/internet/mh.py as Data subclasses, modelled on hip.Lifetime. That is where every nested Info held by a data model lives. It is also the only place Info.from_dict can rebuild them: from mh.py, the import cycle makes from_dict(to_dict()) return an OrderedMultiInfo.
• No alias at the old path. NTPTimestamp gets versionremoved there. PMIPv6Timestamp was beta-only, so it gets none.
• What changes for users. The timestamps are no longer tuples: indexing, unpacking, tuple equality and hashing are gone, and .seconds/.fraction still work. The dumpers now write {"seconds": …, "fraction": …}. versionchanged:: 1.5.0 notes this on both classes and on mh.rst.
• Tuple uses fixed. mh.py:8985 unpacked pmip_timestamp; it now reads attributes. The tests that used tuple(...) do the same.
• Changelog. The 1.5.0 changelog's claim that no NamedTuple remains is corrected, since TCPSegment stays one, and CHANGELOG.md is regenerated to match.

tests/protocols/internet/test_mh_timestamp_info_1886_unit.py covers Info behaviour, byte-exact parse→rebuild, field-keyed JSON and plist output, and pickling at every protocol. It fails 18 subtests on main. Full tests/project: 1005 passed.

Closes #1886

[JarryShaw]

Verdict: GOOD TO GO at ab26e6f81. A Sonnet cross-review checked the change against your ruling on #1869, and I checked the parts it didn't reach.

• The move is needed. Keeping the classes in internet/mh.py makes from_dict(to_dict()) return OrderedMultiInfo for both fields, which the reviewer measured. In the data module the classes are rebuilt, as hip.Lifetime already is.
• No re-export. pcapkit.protocols.internet.mh has no NTPTimestamp/PMIPv6Timestamp. Its private Data_* import follows the module's existing pattern. The moved-name registry is updated, with only NTPTimestamp marked as shipped.
• Round trips are byte-exact. BRR messages carrying each option were built with make() from positional and keyword timestamps across four value sets, and rebuild byte for byte from info and from info.to_dict(). Out-of-range values are still rejected.
• The docs are accurate. PMIPv6Timestamp first appears in v1.5.0b1 and never reached a final release. NTPTimestamp is in every 1.4.x tag.
• Nothing is left relying on tuples. I grepped pcapkit/, tests/, docs/, examples/ and util/.
• The changelog sentence is true. TCPSegment is the only typing.NamedTuple left, and VersionInfo/ModuleDescriptor are collections.namedtuple.
• The tests are real. The new test fails 18 subtests on main, and putting the old unpacking back at mh.py:8985 fails 5 tests across three files.

Not blocking: the byte-exact round-trip test also passes on main, so only the from_dict type check shows why the move was needed.

[github-actions]

Coverage: 90.05% (unit tier, Python 3.15, ab26e6f81, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	2	20	2	96.77%
pcapkit/const	19595	881	2618	867	92.11%
pcapkit/corekit	2462	69	780	35	96.55%
pcapkit/dumpkit	276	3	100	3	98.40%
pcapkit/foundation	2914	164	1016	34	93.59%
pcapkit/interface	138	7	52	5	93.68%
pcapkit/protocols	17411	224	4580	189	98.10%
pcapkit/toolkit	872	177	298	8	77.18%
pcapkit/utilities	512	2	158	4	99.10%
pcapkit/vendor	4407	2342	1010	157	43.27%

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