ci(python): move the KTLO legs into jobs nothing gating waits on (#1738)

[JarryShaw]

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Closes #1738. This implements the owner's option A.

• The move: the KTLO legs of test, integration and pypcap-parity move to test-ktlo, integration-ktlo and pypcap-parity-ktlo. Neither required-checks nor unittest-ordering needs them, so a lost runner or a job-cap hit on a KTLO leg can no longer fail Required checks passed.
• Same steps: each KTLO job runs its twin's steps by YAML alias, so step-level continue-on-error, warning annotations and KTLO summary are unchanged. Job-level continue-on-error: true is a backstop.
• Check names unchanged: all 20 rendered names are identical, and ruleset 23497679 requires none of them.
• No longer runs: on runs 38647800950, 38647748309 and 38622843605, the KTLO legs finished 5–13 minutes before the gating legs.
• Tooling follows: python_versions.py emits the KTLO matrices, ci_timing.py follows the aliased steps, and update_python_versions.py treats a leg moving between twins as a rename. The docs are updated too.
• Tests: test_ktlo_jobs_gate_nothing_1738.py, plus updated 1633/1660/1672/1732 tests.
• Known gap, tracked separately: once 3.11 reaches end-of-life, pypcap-parity has no supported leg.

[JarryShaw]

Verdict: GOOD TO GO at 094d57e20. A Sonnet cross-review re-derived every claim (author: Opus).

• Nothing gating waits on KTLO: every one of the 13 workflows was parsed with PyYAML, and no job needs: a KTLO job. All four workflow_call callers pass gate-only: true, which skips the KTLO jobs.
• Names: all 20 rendered check names are identical on both trees. Each of the 9 KTLO legs appears exactly once.
• Duration: re-measured on three main runs, the KTLO legs finish 5–13 minutes before the gating legs.
• Mutants: four mutants were all caught. They were a gating job needing test-ktlo, project-tests needing it, a dropped job-level continue-on-error, and a renamed KTLO check.
• Tests: new and changed tests fail on main and pass here. actionlint reports nothing new.
• My own re-run in the PR's tree: 1738, unit_tests_queue, 1660, 1672 and ci_timing all pass.
• Follow-ups, non-blocking: pypcap-parity goes empty once 3.11 reaches end-of-life, which I am filing now. engine-tests still runs a KTLO cell inside the gating job. Two YAML constructs, a bare steps: alias and an empty include, are first exercised by this PR's own CI.

[github-actions]

Coverage: 89.69% (unit tier, Python 3.15, 094d57e20, Unit Tests run success)

Package	Statements	Missed	Branches	Partial	Cover
pcapkit (top level)	104	3	20	3	95.16%
pcapkit/const	18860	954	2368	868	91.06%
pcapkit/corekit	2457	69	780	35	96.54%
pcapkit/dumpkit	276	3	100	3	98.40%
pcapkit/foundation	2906	164	1016	34	93.57%
pcapkit/interface	138	7	52	5	93.68%
pcapkit/protocols	17174	225	4588	190	98.07%
pcapkit/toolkit	864	182	298	9	76.33%
pcapkit/utilities	518	2	158	4	99.11%
pcapkit/vendor	4415	2293	1010	160	44.57%

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