chore: lower dart lower bound to 3.7

Author: jpohhhh

example/pubspec.yaml

@@ -3,7 +3,7 @@ description: Demonstrates how to use the fonnx plugin.
 publish_to: "none"
 
 environment:
-  sdk: ">=3.8.0 <4.0.0"
+  sdk: ">=3.7.0 <4.0.0"
 
 dependencies:
   flutter:

pubspec.yaml

@@ -4,7 +4,7 @@ version: 0.0.1
 homepage:
 
 environment:
-  sdk: '>=3.5.0 <4.0.0'
+  sdk: '>=3.7.0 <4.0.0'
 
 dependencies:
   ffi: ^2.1.3