Dart 3.9 / Flutter 3.35 [first LLM release] (#2714)

I got carried away with Gemini and basically rewrote CI and the release
process for the new LLM reality. This work was largely completed by
Gemini.

- Bump all SDK versions to the current beta (3.9.0-0)
- Run `flutter channel beta`
- Wrote `ci_script.dart` to replace the bash scripts
- Converted repository to pub workspace #2499 
- Added llm.md and release.md
- Added redirect for deprecated Samples Index

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

infinite_list/lib/src/api/fetch.dart

@@ -21,7 +21,11 @@ Future<ItemPage> fetchPage(int startingIndex) async {
   // If the [startingIndex] is beyond the bounds of the catalog, an
   // empty page will be returned.
   if (startingIndex > catalogLength) {
-    return ItemPage(items: [], startingIndex: startingIndex, hasNext: false);
+    return ItemPage(
+      items: [],
+      startingIndex: startingIndex,
+      hasNext: false,
+    );
   }
 
   // The page of items is generated here.