docs(protocols): second whole-repo pass over application, misc and the protocol base (#1103)

[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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Summary

#1103 second whole-repo pass, application slice.

Version directives, 1.1.0-1.4.1 backfill:

• Protocol: versionchanged 1.3.0. The built-in families moved onto
  ProtocolBase, so a built-in protocol is not an instance of Protocol,
  and a Protocol subclass registers itself in pcapkit.protocols.proto.
• data.misc.raw.Raw: versionchanged 1.3.3. packet left its fields when the
  base data class took it over, so the constructor takes protocol and
  error only.

Accuracy:

• ProtocolBase.unpack: since fix(protocols): ProtocolBase.pack() without keywords replaces the instance's header #1769, pack() sets header only on the
  call post_init makes during construction, so the note names that
  call and from_schema() rather than pack() in general.
• HTTP.make: Returns said bytes; it returns the versioned make()'s schema.
• pcapkit.protocols.proto: the values are ProtocolBase subclasses,
  and the built-in ones are not Protocol subclasses.

AST guard identical on all four files; tests/project and the pack, HTTP
and docstring-contract tests pass.

Refs #1103

[JarryShaw]

Verdict: GOOD TO GO at ec2afbc80. A Sonnet cross-review (author: Opus) found no blocking findings. Scope stays inside the slice, the AST guard is identical against main, and every directive was checked against the release tags. The merged build of all nine second-pass heads has 18 warnings, the same as main. tests/project: 950 passed, 1 skipped, 3 warnings, 3670 subtests passed..