Add executable transport adapter conformance guards

[smiggleworth]

Summary

• publish a dependency-free @askrjs/server/testing adapter conformance runner
• verify real-adapter response cancellation and incomplete-request timeout exercises under bounded deadlines
• provide stable diagnostics, cleanup signals, frozen success evidence, public types, and package-artifact guards
• document adapter ownership and a reusable real-transport integration pattern
• source-audit @askrjs/node and track its real-socket adoption in Adopt real-socket adapter cancellation and timeout conformance guard askr-node#23

Linked issue

Closes #20

TDD

• Red 20c49d6: the required public testing entry point and conformance behavior did not exist.
• Green 8699b25: 12 focused success/validation/failure/deadline tests pass with the new runner and packaged subpath.

Guardrails

• cancellation is observed from the supplied infinite ReadableStream, not inferred from callback completion
• each adapter exercise and cancellation observation has a bounded deadline
• cleanup signals fire on success/failure/timeout
• stable error codes distinguish thrown exercises, hanging exercises, and missing cancellation
• emitted types, package exports, and packed files are standing contract gates

Acceptance audit

• Every acceptance criterion in Missing adapter-author guidance: stream cancellation on abort and timeout enforcement #20 is checked with evidence.
• Focused red suite failed because the contract was absent and passes at green.
• Full unit, type, build, package-artifact, audit, and exact-head hosted CI gates pass.
• Exact squash merge, tag, publish workflow, and clean registry consumer are verified.

Verification

• npm run check
• npm audit --omit=dev

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[smiggleworth]

Release closure verified:

• squash merge 675da89d7eee5fb50590f49a7f1ee798623c1db8
• publish workflow run 31906905221 passed all three CI lanes and the publish job at that exact SHA
• annotated tag v0.0.18 peels to the merge SHA
• npm serves @askrjs/server@0.0.18 with integrity sha512-PMy1dO9TfFx2tqYMMC5e0DBUhR/kTJCStmJSc1U20A1k/pEe/YMRCfqB7KcC8kJJfVa1vjx+j4ZkkIo7k0Xhlg==
• a clean packed consumer and the askr-node registry install both imported @askrjs/server/testing; the clean consumer ran each exercise once, received the frozen success report, and audited with zero runtime vulnerabilities
• reference-adapter adoption is active in Adopt real-socket adapter cancellation and timeout conformance guard askr-node#23 / PR Add executable transport adapter conformance guards #24, where the shared real-socket guard has already exposed and driven a timeout-enforcement fix