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

[JarryShaw]

Please follow the guide below

• You will be asked some questions, please read them carefully and answer honestly

• Put an x into all the boxes [ ] relevant to your pull request (like that [x])

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• Searched for similar pull requests

• Followed the coding style (make pylint, make mypy, make isort)

• make test passes, and a test case covers the change. Narrow runs only, listed below.

• 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

What is the purpose of your pull request?

Tick the commit type your subject line carries.

• fix — corrects a defect
• feat — adds a feature
• perf — changes performance, not behaviour
• refactor — changes neither behaviour nor performance
• test — tests only
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• ci — workflows or build tooling
• release — bumps the version or rolls up a distribution
• chore — anything else

The fourth whole-repo prose pass of #1103, over the application and misc protocols and the protocol base. It changes prose only: every changed .py file's AST is unchanged once string expressions are blanked, except where a docstring is added or vendor template text is edited together with its generated const file.

Accuracy:

• PCAP-NG registry comments describe what a value is: a str naming the
  read/make methods, falling back to the *_unknown pair, or a
  (parser, constructor) pair; they claimed a single parsing method.
• _EnumRegistry.missing gets its own docstring; it rendered the
  inherited defaultdict pseudo-code, which describes inserting a miss.

Wording:

• "c.f." becomes "see" (or "compare" where a comparison is meant), and
  "&" becomes "and", in the next-layer registry comments.
• Module docstrings and their pages read "implements an extractor for".
• Raw.post_init and a PCAP-NG schema docstring lose garbled clauses.

Counts:

• A comment in ProtocolBase._make_index no longer counts lines.

Refs #1103

[JarryShaw]

GOOD TO GO at 4ecbdc432. A Sonnet cross-review found no accuracy, count, timed-context or markup problems. The AST guard shows prose-only changes, and tests/project, the tier guard and the docstring contract pass.

[github-actions]

Coverage: 90.07% (unit tier, Python 3.15, 4ecbdc432, 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	2504	70	792	36	96.54%
pcapkit/dumpkit	276	3	100	3	98.40%
pcapkit/foundation	2916	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	522	2	158	4	99.12%
pcapkit/vendor	4431	2341	1018	156	43.64%

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