refactor(http): move test_start_line and its patterns into the http base module (#1519)

[JarryShaw]

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• Move: httpv1._test_start_line becomes the public http.test_start_line, listed in http.__all__. HTTP._guess_version now calls it directly; the lazy import from httpv1 is gone.
• Shared patterns: _RE_METHOD, _RE_VERSION, _RE_STATUS and _HTTP2_PREFACE_HEADER move with it and stay private. httpv1 imports them from http, the direction it already imported in, so there is still one copy of each and no new cycle.
• Docs: test_start_line is documented on the http page and removed from the httpv1 page. Docstrings that cited the old location are updated, including three in tests/const/test_const_method_value_lookup_908_unit.py. The existing changelog entries are left as they are.
• Tests: test_http_unit.py now imports the predicate from http. The new test_http_test_start_line_1519_unit.py (6 tests) pins request lines, status lines, the HTTP/2 preface refused, non-HTTP refused, the shared pattern objects and the direct call. All 6 fail on origin/main and pass here.
• Byte-identical: for every frame in all 23 sample captures (1,616 frames, 241 HTTP layers: 231 HTTP/1.1, 10 HTTP/2), the protochain, HTTP version and canonical to_dict() JSON match origin/main exactly. Both snapshots have sha256 2bb6b450….

Ran one at a time: tests/protocols/application, tests/project, tests/test_docstring_contract.py, tests/test_tier_guard.py, and the edited tests/const module. All green. The Sphinx build reports no warnings from the HTTP pages.

Refs #1519

[JarryShaw]

Verdict: GOOD TO GO at a063c5896. Cross-reviewed on Sonnet; the author ran Opus.

• Unchanged code: test_start_line and the four patterns are AST-identical to main, including every regex string. httpv1 now reuses http's pattern objects (is holds).
• No import cycle: at module level, http.py imports nothing from httpv1 or httpv2.
• Behaviour: classification and to_dict() are byte-identical on main and the PR across 1,616 frames and 241 HTTP layers. 4,057 edge and fuzzed payloads give identical outputs on both trees. On every one, the predicate's answer matches the parser's: 1,217 accepted, 2,777 refused.
• Tests and docs:
  • Fail-before: 6 failures.
  • pytest does not collect the library function.
  • The two HTTP doc pages build with the same warning set as main.

[github-actions]

Coverage: 90.08% (unit tier, Python 3.14, a063c5896, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	4	20	4	93.55%
pcapkit/const	18795	843	2356	756	92.08%
pcapkit/corekit	2161	66	700	33	96.26%
pcapkit/dumpkit	242	2	88	2	98.79%
pcapkit/foundation	2665	98	934	42	95.00%
pcapkit/interface	112	7	40	5	92.11%
pcapkit/protocols	17086	238	4628	190	97.98%
pcapkit/toolkit	539	74	168	3	84.58%
pcapkit/utilities	431	4	124	4	98.56%
pcapkit/vendor	4409	2342	1006	157	43.25%

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