Fix optional react-dom loading in mobx-react-lite

[cyphercodes]

Fixes #4663

Summary

• Replace the static react-dom re-export in mobx-react-lite with a guarded optional load.
• Fall back to the existing no-op batch scheduler when react-dom is unavailable.
• Add a regression test that verifies mobx-react-lite can load when react-dom cannot be resolved.

Code change checklist

• Added/updated unit tests
• Updated /docs (not applicable: bug fix, no docs/API change)
• Verified that there is no significant performance drop (not applicable to core MobX performance; ran targeted package checks and size test)

Verification

• npm ci --ignore-scripts
• npm -w mobx run build:test
• npm -w mobx-react run build:test
• npm -w mobx-react-lite run lint
• npm -w mobx-react-lite run test:types
• npm -w mobx-react-lite run build:test
• npm -w mobx-react-lite test -- --runInBand
• npm -w mobx-react-lite run test:size
• npx prettier --check packages/mobx-react-lite/src/utils/reactBatchedUpdates.ts packages/mobx-react-lite/__tests__/optionalReactDom.test.ts
• git diff --check
• Built CJS smoke test with react-dom module loading blocked

[changeset-bot]

🦋 Changeset detected

Latest commit: 76ad2c7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
mobx-react-lite	Patch

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[kubk]

Thank you for the PR. As described in the issue comments - the problem shouldn't be solved at all as React 18+ provides its own batching. Mobx v7 will drop React <=17 support: #4671