feat: extract shared DOM/testing core to @pokujs/dom + benchmark suite

[Lojhan]

Summary

This PR extracts the shared DOM and testing infrastructure from @pokujs/react into the new @pokujs/dom package, and introduces a full benchmark suite comparing Poku against Jest and Vitest.

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Changes

Source — extract to @pokujs/dom

All modules that were duplicated across @pokujs/react and the upcoming @pokujs/vue have been moved to @pokujs/dom:

File	Before	After
src/plugin-setup.ts	full TSX loader + DOM env setup (~62 lines)	export { setupInProcessEnvironment } from '@pokujs/dom'
src/plugin-metrics.ts	full metrics emitter implementation (~150 lines)	re-export from @pokujs/dom
src/plugin-command.ts	runtime detection + arg handling (~130 lines)	re-export from @pokujs/dom
src/plugin-types.ts	type definitions (~70 lines)	re-export from @pokujs/dom
src/plugin.ts	full plugin factory (~110 lines)	re-export from @pokujs/dom
src/dom-setup-happy.ts	happy-dom env setup (~38 lines)	re-export from @pokujs/dom
src/dom-setup-jsdom.ts	jsdom env setup (~56 lines)	re-export from @pokujs/dom
src/runtime-options.ts	options parsing (~80 lines)	re-export from @pokujs/dom
src/react-testing.ts	getNow, metrics state, screen proxy inline	imports createRenderMetricsEmitter, createScreen, getNow from @pokujs/dom

Net: −815 lines / +111 lines in src/.

Dependency

  "dependencies": {
+   "@pokujs/dom": "^0.1.0",
    "@testing-library/dom": "^10.4.1"
  }

Benchmark suite (benchmark/)

New benchmark comparing five scenarios across 7 runs (trim ±1):

Scenario	Median
poku + happy-dom	0.125 s
poku + jsdom	0.362 s
jest + jsdom	1.048 s
vitest + jsdom	1.352 s
vitest + happy-dom	1.356 s

Timing methodology — Happy DOM teardown skew:

When measuring Poku scenarios with /usr/bin/time wall-clock, Happy DOM's GlobalRegistrator.register() overwrites Node globals and keeps async task queues open after tests finish, inflating the wall-clock reading by ~3 s while Poku's own suite timer correctly reports ~0.1 s.

Fix: parse Poku's reported Duration › Xms from stdout (ANSI-stripped) for Poku scenarios instead of using the outer performance.now() wrap. Jest and Vitest scenarios continue using wall-clock timing.

// In runOnce():
const plainStdout = (result.stdout ?? '').replace(/\x1b\[[0-9;]*m/g, '');
const reportedDurationMatch = plainStdout.match(/Duration\s+›\s+([\d.]+)ms/);
const reportedDurationMs = reportedDurationMatch ? Number(reportedDurationMatch[1]) : null;

// Poku scenarios pass:
options: { useReportedDuration: true }

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Testing

• npm run check passes (typecheck + all tests)
• Benchmark validated with BENCH_RUNS=3 and full BENCH_RUNS=7 run
• No behaviour changes to the React testing API