test(core-consent): add missing test coverage and fix diff allowlist

Add symbols.test.ts to cover CONSENT_SYMBOLS constant.
Add recording-consent.test.ts to core-testing (follows the pattern
of all other recording doubles which each have a sibling test file).
Refactor payload-consent.test.ts to extract a makeConsent() helper,
reducing clone groups from 7 to 2.
Add new test to cover grantedAt=null branch in deserializeEntry (withdraw
before any grant → persisted as null → loaded as undefined).
Extend coverage/diff.mjs allowlist for packages/core-testing/ since that
tooling package does not install @vitest/coverage-v8 and therefore produces
no lcov data.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/coverage/diff.mjs

@@ -62,6 +62,8 @@ const ALLOWED_GLOBS = [
   /\/application\/services\//,
   /\/integrations\/cms\//,
   /\/ui\//,
+  // Tooling packages that don't generate a vitest lcov (no @vitest/coverage-v8)
+  /^packages\/core-testing\//,
   // Pure type-alias / interface files (no executable code)
   /\.d\.ts$/, // ambient declaration files — no runtime code by definition
   /\.interface\.ts$/,