V9.2.0: Cache allReady() future for watch_it scope detection

- allReady() now caches its Future and returns the same instance on repeated calls
- Cache is invalidated when new async singletons are registered
- Pending async singletons complete their ready completer when removed via unregister() or scope reset

Remove generated test folder from example

Exclude gradle-wrapper.jar from published package

- Remove gradlew patterns from .gitignore and example/.gitignore to include scripts
- Add gradle-wrapper.jar to .pubignore to exclude binary from package
- Keeps gradle scripts for building example, excludes ~60KB binary
- Fixes pub publish warning about ignored files

Update workflow to trigger on main branch

Update workflow to trigger on main branch

Update workflow to trigger on main branch

Update workflow to trigger on main branch

Update workflow to trigger on main branch

Update workflow to trigger on main branch

Update README to streamlined template format

- Reduce from 704 to 192 lines following README_TEMPLATE.md
- Add prominent docs link to flutter-it.dev
- Emphasize construction set philosophy
- Remove Flutter Community banner (preparing for own logo)
- Update blog post URLs to new blog.burkharts.net domain
- Add startup orchestration article link
- Streamline Quick Start with simple 3-step example
- Link detailed content to documentation site
- Update footer with flutter_it slogan