Update changelogs from fern repo (#3603)

Co-authored-by: iamnamananand996 <31537362+iamnamananand996@users.noreply.github.com>

Author: fern-support

fern/products/sdks/overview/python/changelog/2026-02-12.mdx

@@ -0,0 +1,6 @@
+## 4.57.0
+**`(feat):`** Add `custom_transport: true` config option for SDK developers to expose an `http_client`
+override parameter on generated client constructors. This allows SDK developers to provide
+custom httpx transports via custom code (e.g., factory methods like `ValidationClient`).
+
+