docs(const): drop version directives from generated tables (#1884)

[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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• Removes the version directives from the template text of the ftp/command, http/method, ipv6/extension_header, pcapng/option_type, pcapng/tls_key_label, reg/apptype/apptype and tcp/flags crawlers. The same blocks come out of the committed const modules, with no re-crawl.

• Each note moves onto its hand-written page under docs/source/pcapkit/const/, as fix(const)!: name LLACode codes 0 and 2 as RFC 5568 does (#1848) #1872 did, keeping the original version.

• Directives on the crawler framework's own code stay. That covers pcapkit/vendor/__init__.py, __main__.py and default.py, plus the apptype crawler's own wrap_comment and tabulate methods, since none of them is template text.

• tests/project/test_no_version_directives_in_generated_tables_1884_unit.py finds template text by parsing each crawler, not from a list of exempt files. It fails on main and passes here.

• tests/vendor, tests/const, tests/project and the tier guard pass. No Sphinx build was run.

Closes #1884

[JarryShaw]

Verdict: GOOD TO GO at 5cfa5a46b. A Sonnet cross-review confirmed the following:

• Every removed directive sat in emitted LINE/BASE template text, and came out of its const file identically.
• The directives that stay are on hand-written framework code that never reaches a const module.
• Every moved note keeps its version and facts.
• The new test fails on main, catches a directive re-added to a template, and ignores one added to a crawler method's docstring.
• tests/vendor, tests/const, tests/project and the tier guard pass.

Two gaps, neither blocking. The regex at :42 would miss .. versionchanged:: written with two spaces, or one split across a +. And no Sphinx build of the const pages was run.