build: bump MTG to 20250915.1 (#688)

This PR updates the generator version to `1.0.0-alpha.20250915.1` and regenerates the library. The `azure-tools/typespec-azure-core` dependency was removed from MTG, and since I found no reference to it in this library, I also removed it as a dependency here.

Author: jorgerangel-msft

codegen/generator/src/OpenAI.Library.Plugin.csproj

@@ -8,7 +8,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="Microsoft.TypeSpec.Generator.ClientModel" Version="1.0.0-alpha.20250905.1" />
+      <PackageReference Include="Microsoft.TypeSpec.Generator.ClientModel" Version="1.0.0-alpha.20250915.1" />
     </ItemGroup>
 
   <!-- Copy output to package dist path for local execution and  -->

codegen/package.json

@@ -29,11 +29,10 @@
   ],
   "dependencies": {
     "@open-ai/plugin": "file:",
-    "@azure-tools/typespec-client-generator-core": "0.59.0",
-    "@azure-tools/typespec-azure-core": "0.59.0",
-    "@typespec/http-client-csharp": "1.0.0-alpha.20250905.1",
-    "@typespec/http": "1.3.0",
-    "@typespec/openapi": "1.3.0"
+    "@azure-tools/typespec-client-generator-core": "0.60.0",
+    "@typespec/http-client-csharp": "1.0.0-alpha.20250915.1",
+    "@typespec/http": "1.4.0",
+    "@typespec/openapi": "1.4.0"
   },
   "devDependencies": {
     "@types/node": "^22.8.1",