chore(deps): add PyYAML to the test extra (#1076)

[JarryShaw]

• 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
• Added a changelog entry — 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?

• chore — anything else

---

Description

Adds unpinned PyYAML to the test extra only (not runtime; pcapkit never imports yaml), so the yaml.safe_load cross-checks run on every CI leg that installs .[test]. Also rewrites the docstrings and skip messages in four tests/project modules that said PyYAML is in no extra. These are prose-only changes: with strings stripped, the AST matches main.

Measured in a fresh 3.14 venv, without vs with PyYAML, skips per module: test_project_status 4 → 0, test_release_gates 3 → 0, test_bump_version 1 → 0. tests/test_tier_guard.py: 109 passed. tests/project: 375 passed, 1 skipped (#930, unrelated). Lint and the full suite were not run.

test_project_status.py:231 carries the same stale claim; it is left to #1077.

Closes #1076

[JarryShaw]

Cross-review verdict on 14c30ed08: GOOD TO GO (ran on Sonnet; author Opus)

• PyYAML is now in the test extra only. pcapkit/ never imports yaml, and the comment lists all four modules that do.
• With .[test] installed, tests/project goes from 365 passed / 11 skipped to 375 passed / 1 skipped. All 10 PyYAML skips now run; the remaining skip is the unrelated refactor(const,protocols): reparent the last seven non-registry enums onto EnumLookup #930 one.
• The four changed files are AST-identical to main once strings are blanked, so only prose changed.
• No lockfile, constraints file or _dependency_gates entry needs updating. test_tier_guard passes (109).
• The reviewer's one finding is the stale "PyYAML is in no extra / CI has no PyYAML" prose in test_project_status.py (lines 231, 242 and 532). test(project-status): guard container/services options and working-directory against expressions (#1077) #1079 owns that file and already rewrites all three sentences, which I checked in its diff. I split them that way deliberately. Merge order does not matter.
• UNVERIFIED: the reviewer could not run make_samples.py (no scapy in the throwaway venv). Nothing in this diff depends on the samples.

[github-actions]

Coverage: 88.74% (unit tier, Python 3.14, 14c30ed08, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	4	20	4	93.55%
pcapkit/const	18757	1035	2342	846	90.23%
pcapkit/corekit	1874	91	578	22	94.33%
pcapkit/dumpkit	136	0	40	0	100.00%
pcapkit/foundation	2422	143	842	34	92.62%
pcapkit/interface	112	7	40	5	92.11%
pcapkit/protocols	15653	187	3942	162	98.19%
pcapkit/toolkit	487	71	144	3	84.15%
pcapkit/utilities	429	4	122	4	98.55%
pcapkit/vendor	4409	2359	1006	158	42.84%

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