Roll Dart SDK from c7518d480c73 to 83c6b6124380 (1 revision) (flutter#175064)

https://dart.googlesource.com/sdk.git/+log/c7518d480c73..83c6b6124380

2025-09-08 dart-internal-merge@dart-ci-internal.iam.gserviceaccount.com
Version 3.10.0-181.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
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Author: engine-flutter-autoroll

DEPS

@@ -56,7 +56,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/main/DEPS
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': 'c7518d480c736956ae21447b6d84157693639f7b',
+  'dart_revision': '83c6b612438015f61b641fa2f7d8f128f85353a0',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py