feat: configure streamed hydration behavior

[janechu]

Pull Request

📖 Description

Adds hydration configuration for streamed Declarative Shadow DOM:

• Adds noopAfterHydrationComplete to enableHydration() so streaming apps can keep hydration active after the initial batch.
• Preserves the default behavior of no-oping for later prerendered batches after hydrationComplete.
• Adds tests and an ecosystem fixture for late-appended hydratable DSD with reactive binding updates.
• Updates README, design/API docs, website docs, export sizes, and Beachball change file.

👩‍💻 Reviewer Notes

Please review the default no-op behavior versus noopAfterHydrationComplete: false for streamed DSD scenarios.

📑 Test Plan

• npm run build ✅
• npm run biome:check ✅
• npm run checkchange ✅
• npx playwright test src/components/hydration.pw.spec.ts from packages/fast-element ✅
• npx playwright test --config=playwright.declarative.config.ts test/declarative/fixtures/ecosystem/hydration-config/hydration-config.spec.ts from packages/fast-element ✅
• npm run test ❌ failed in @microsoft/fast-test-harness Firefox tests with 5s navigation/setup timeouts unrelated to the hydration changes.

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.