rollback smithy-rs to 2025-08-13 (#1344)

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## Motivation and Context
Rollback smithy-rs update
(#1343). This is causing an
issue with internal performance testing steps in our release pipeline
(not performance related but due to Cargo and versioning (internal ref:
`P288989567`).

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choice.

Author: aajtodd

config.json

@@ -1,5 +1,5 @@
 {
   "dependencies": {
-    "smithyRsVersion": "release-2025-08-18"
+    "smithyRsVersion": "release-2025-08-13"
   }
 }