update changelogs

Author: chdeskur

fern/products/cli-api-reference/cli-changelog/2025-12-23.mdx

@@ -1,3 +1,7 @@
+## 3.31.1
+**`(fix):`** Fix double JSON.stringify in dynamic IR upload, reducing memory usage and ensuring correct Content-Length header calculation with Buffer.byteLength.
+
+
 ## 3.31.0
 **`(fix):`** Add a `--dynamic-ir-only` flag to SDK generation to enable access to dynamic snippets from SDKs without regenerating the entire SDK.