fix(dom): keep readiness gate async-free so TestCafe t.eval accepts the bundle

[prklm10]

Fixes PER-10121

Root cause

The @percy/dom bundle is injected into the browser verbatim by SDKs. @percy/testcafe/index.js:29 does:

await t.eval(new Function(await utils.fetchPercyDOM()), { boundTestRun: t });

TestCafe's t.eval/ClientFunction machinery statically rejects any async/await or generator syntax in the evaluated source.

The readiness gate shipped in 1.31.14 (PER-7348, #2184) added two async functions — runAllChecks and waitForReady in packages/dom/src/readiness.js — which are the only async/await in the entire dom source. Because the rollup babel target (browsers: ['last 2 versions and supports async-functions']) intentionally does not down-level async, those tokens flow straight into dist/bundle.js. Every @percy/testcafe snapshot then fails with:

eval code, arguments or dependencies cannot contain generators or "async/await" syntax (use Promises instead).
  at percySnapshot (node_modules/@percy/testcafe/index.js:29:13)

and the build finalizes with Failure: Snapshot command was not called. Playwright/other SDKs are unaffected because they don't route the bundle through TestCafe's restrictive evaluator.

Bundle token profile (published):

Version	size	async	await	generators
1.31.13 (last good)	47 KB	0	0	0
1.31.14	101 KB	2	2	0
1.32.4 (latest)	105 KB	2	2	0

Fix

Rewrite runAllChecks and waitForReady to explicit Promise chains (return Promise.all(...), Promise.race(...).catch(...).then(...)). Behavior is unchanged — both were already Promise-returning at every call site (runAllChecks(...).then(...), await waitForReady(...)), and the try/catch → .catch/.then mapping preserves the timeout/abort/post-processing semantics exactly. The rebuilt bundle is back to 0 async / 0 await / 0 generators, matching the 1.31.13 profile that TestCafe accepts.

Add a package-local packages/dom/src/.eslintrc that forbids async/await/generators via no-restricted-syntax, so this browser-injection contract can't silently regress again (which is exactly how it shipped).

Testing

• Full @percy/dom suite green: 902 tests pass, including the readiness suite (waitForReady returns a Promise, stays sync even when readiness config is present, timeout/graceful-degradation cases).
• Rebuilt dist/bundle.js verified async/await/generator-free.
• ESLint guard verified: fails an async sample with the PER-10121 message, passes the rewritten readiness.js.

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